Well, hello there, OP. As a veteran of AH.com, and someone who's been considering writing a couple of these TLs, I think I can help you with a few things.
For starters, I think it goes without saying that you want to avoid
the worst CSA-related cliches, like slavery ending voluntarily for example, but there's also a few other questionable cliches-and other, less common tropes-that would be best avoided.
1. The Confederacy as a wholly prosperous, and highly modern nation-Yeah, this is definitely one you'll want to avoid; too many CSA TLs have gone with this assumption, including many of them on this site. While
@Leviticus does raise an interesting point in their most recent post:
It's also true that even though the CSA might not entirely reject modernity, my counterpoint here would be that one could still reasonably expect that there would be a lot of things holding back the Confederacy from becoming a truly prosperous nation(including, yes, the continued existence of slavery, and not
just because of sanctions, etc.), instead of one that lags behind most/all of the rest of the West, and is heavily stratified(if not extremely so), with prosperity only residing in the hands of a powerful few, with little in the way of a middle class and lots of poorer citizens, even if it manages to survive all the way to the present day or close to it.
2. Strongly nativist Union(or at least more so than IOTL)-Yes, definitely avoid this one, too, if you can. Don't get me wrong, nativism(and racism in general) will, sadly, be somewhat of an issue regardless, but this cliche has popped up in a number of TLs that I have observed despite there not being any truly plausible basis for this, in pretty much any of them. Yes, one can point to the Chinese Exclusion Act, etc., but it's worth pointing out that, to a point, the severity, at least, of certain aspects of restrictionism were peculiar to OTL and a number of things could have changed for the better without
that much difficulty.
And depending on the POD, you can even significantly reduce anti-Chinese racism in California and other Western states + territories without too much trouble
before the 1880s or even by the outbreak of the war.....though there might have to be some major incident that discredits the local anti-immigration fanatics; maybe an out of the blue massacre or two, and/or some of them are caught aiding and abetting the Confederates? Both of these things are quite a bit more plausible than many might realize, FWIW. (Sadly, though, it's also true that anti-Asian racism could fairly easily have been worse east of the Rockies, and doing the former
and avoiding the latter at the exact same time might well be genuinely difficult to do plausibly).
3.The Confederacy as a popular immigration destination-Nope. If even the re-unified U.S. IOTL was going to fall for widespread immigration restrictions, then why would the Confederacy would be any more lenient overall? In all likelihood, they'd be even more restrictive overall: as
@NedStark correctly pointed out, the South was a hotbed of anti-immigration sentiment IOTL, and I would add, even in Florida and Louisiana(several Italian-Americans were once lynched in La. in the 1890s-sometime in 1891, IIRC?). The doesn't mean all immigration would be banned straight away, but it's not hard to see the C.S.A. clamping down on it early on in it's history, and even Western European Catholics(maybe even the French included) could be subject to severe restrictions, perhaps even based on ethnicity. And Orthodox immigrants wouldn't be treated too much better, not even Greeks(if significant anti-Greek discrimination could exist even in places like Omaha, NE IOTL, it could certainly be a problem in an independent South!).
That said, though, you might be able to make some exceptions-Confederates wouldn't necessarily be opposed to British-especially English-immigration, and certainly, at least Protestant Germans wouldn't be turned away, either, unless relations between the C.S. and these countries were really bad. (If you wanted to make things a little more interesting, you could try having the C.S.A. attract some immigrants from the Netherlands, Belgium or even Luxembourg, though Scandinavia might be pushing it a little too hard)
4. Predominantly Progressivism-based racial/ethnic based immigration restrictions, etc.-This one shouldn't be too hard to sidestep. Even IOTL, Progressives were no more likely than anti-Progressives to be opposed to large-scale immigration of people who weren't WASPs or others of northern European(and Protestant) extraction, and in some cases less so, and much the same also goes for racism, etc.; If anything, it would make more sense for the contrasts to be rather starker ITTL, and without the South to worry about, both nativists and the anti-Progressive types wouldn't have been as empowered(thus fewer of TTL's Progressives would then, plausibly, feel as inclined to appease devoted racists, nativists, etc.).
5. Britain and France, in particular, becoming longtime Confederate allies-This mainly only seems to come up because of Harry Turtledove's famous TL-191 series; while it may not
necessarily be
wildly implausible, it's just unlikely enough that this trope may be better avoided altogether, especially because Britain, especially, had just eliminated slavery in it's empire a couple decades earlier, and I doubt even many moderate[1a] Britons, let alone most liberals[1b], would have been happy with even rumors of a concrete alliance with a bunch of slavers.....so I'd recommend against this one, too, unless you really want to go for it.
That's not to say that the C.S.A. can't have European allies, but honestly, if one wants to go there.....why not go for at least Prussia and/or Germany, or even Austria-Hungary? Might be a bit harder to do the latter, since A-H
was a majority Catholic country, but at the very least, not that hard to see the C.S.A. buddying up with Prussia or a conservative Germany at some point(depending on if German unification is butterflied or not)-there would be a potential complication in the person of Otto von Bismarck but removing him from power could make a crucial difference-maybe by 1880 or so? (I'd also suggest even considering Russia, but this would have to be after the passing of Alexander II, though, whenever that happens.)
6. The U.S. and C.S. as longterm friends, not just neighbors-Unless the Union is successfully taken over by a hard-right[1d] or even reactionary series of administrations for an extended period, this almost certainly wouldn't happen, and in fact, many liberal[1e] Americans, especially, would want revenge for the Union being broken apart; that would not only not heal anytime soon, but might in fact, last as long as the Confederacy itself does.
[1a, b, c, d, e]Yes, I know some may question the use of these word, but it's in relative terms, and they can be, and sometimes are, significantly more useful than many may realize(at least from the late 18th century and onward, anyway, if nothing earlier).
7. More widespread anti-black racism in the Union than IOTL-I've seen this trope crop up a few times as well, and it's another one that's of dubious plausibility at best; really do try to avoid this one if you can! Yes, racist backlash would eventually occur at some point, but to keep this short: in a world in which people have to be regularly reminded of the horrors of Confederate brutality, it very likely wouldn't be as effective in actually screwing over African-Americans as it sometimes was IOTL, in terms of
overall discrimination, etc.; that's not to say that the
severity of racism, per se, would
always be less: in fact, it's possible that devoted racists-like nativists-could be even more overtly nasty in a U.S. where their influence was diminished relative to OTL(though that would eventually probably lead to even more pushback against them).
8. The World Wars, etc. turning out exactly as they were in our world-Mainly including this here because it's perhaps the most common trope overall, and just not for CSA victory timelines. Hey, I'm not saying you can't have a World War or two(or, heck, feel free to call 'em something else if you'd like!), and they can even happen in the same general time frame-it's just that it's a
bit unlikely that Gavrilo Princip would still be able to shoot Archduke Franz Ferdinand, in that same exact city-that being Sarajevo-on the exact same day as IOTL with a POD circa 1860, so it might not hurt to take that into consideration, ya know?(That said, though, to be quite fair, a few bits of OTL history repeating, at least in a way, may not hurt your TL's plausibility that much-especially early on-provided it's not really overdone; though it can depend on the exact POD, and the likely magnitude of changes since then).
9. Ignoring non-state actors, and their use by nation-states-That's also a topic you may want to cover at some point, too; I kind of already mentioned the possibility of the C.S.A. being assisted by anti-immigration forces given an early enough POD, but nothing says said elements couldn't be manipulated
afterwards, either. And it's more than possible that underhanded espionage by both sides could very well spark a major diplomatic incident or two, if not even a new war.
10. Repeating the use of OTL figures beyond a certain point-Okay, this isn't necessarily a
bad thing, per se. But it also wouldn't necessarily be terribly likely for figures like, say, Barack Obama or George Bush to show up with a POD around 1860, especially if it's one that's liable to have a major short-term impact on the world-it's OK if you want to keep that sense of familiarity, but I really would sincerely recommend you try to find a point to start using fictional characters. (A rule of thumb I like to use is, I adjust it based on both the time the POD occurred and the magnitude of the POD in question)
Also, some general tips that I hope are also helpful:
1. In regards between convergence and divergence, don't be afraid to strike a balance between the two(but also, not relying too much on OTL history!)-Having been in this genre for over a decade myself, I can tell you that it can be a genuinely daunting task finding an optimal balance on a number of things, including on this topic. But honestly, don't worry too much if you can help it-if nothing else, just go with the flow, and then revise if/when necessary. To expand on this a little, while I've kinda already covered a few examples of OTL history that you might
not want to repeat ITTL, that doesn't mean you have to radically change every little thing-for example, television can still be called television, the Internet can still be the Internet, etc., unless you really wanna go out of your way to make new and/or original terms(and some have).
2. Research is your friend-Yeah, this one is pretty straightforward, but do be careful with sourcing, as not everything you'll find is necessarily good quality(and sometimes you may just find utter crap).
3. Don't be afraid to take feedback into account-I think this is important, too. Even if you may not agree with the other person, at least try to acknowledge their viewpoint-though don't be afraid to correct somebody if you're at least reasonably certain or you know for sure that they're wrong about something.
4. Formatting is up to you-There really are many ways to write a TL-in chronilogical order or skipping and jumping between time frames.....many different ways you can set up TTL references(you can look at published works like Sobel's
For Want of a Nail, or Internet originals like
Look To The West or
Lands of Red and Gold, for examples!).....and that's only for starters.
5. Just try to have fun-As it says on the label. At the end of the day, this is
your project and don't be afraid to enjoy yourself.