First let me say: thank you SmokeNLark for confirming on the Harlequins and the Peppered Cories.
Yepp, I'm fully accepting and prepared for the possibility that the shrimp might be seen as food. I was thinking of doing a trial of sorts to see how each of them take to shrimp -- if they're all fine with them then I would like some in each tank, because I think they're neat. I'm not going to hold my breath with Bebette, however. I do plan to start with Ghosts since they're inexpensive and more readily available, and if they are picked on I plan to set up one of the small tanks as an NPT as well for them rather than return them.
As for ADFs, yea, I know they'll need a little special care but they're too neat to pass up if I can keep them in one of the tanks. My brother and I have always been big into frogs and other amphibians, so it'd be neat to have some again, even if they are tiny, haha. Hopefully they don't get picked on either.
All right, so the Harlequins are a good possibility then: good to know. After a little more research it seems that Mosquitos should be fine as well as far as fin-nipping goes. I'm getting some conflicting information on the Galaxies/CPDs as regards their suitability, but I know that a local place has them in a community tank and they weren't trying to hide or acting nervous so I'm thinking they would be fine, especially in an NPT. But I might ask and see if they might be fin-nippers.
As for the Kuhlis, another site states that five would be fine in a 10-gallon. I think I'll look into these guys a bit more though -- I do think they're neat, and my brother told me that I should get an eel: these guys are about as close as I'll get for a while.
I know a lot of people like snails, but I'm just not a big fan -- they're interesting in small doses, but anything more than that and I kind of don't really care. I lose interest and move on. As for the Platties, I kind of don't want anything that would compete with or outshine my Bettas, haha. I want them to be the leading role, and the rest the supporting cast I guess. But, just as with any good movie, the supporting cast still needs to be interesting for it all to work.
Finally, as far as the Plan B goes: I'll be setting these up one or two at a time, so I'll have a chance to see how things go before getting too far along. I'll probably get one started and see how that goes before I start up the next one, and repeat the process once more (the divided cube will be last as I need to build a stand for it first) if things are going well at that point. I'll always have the smaller tanks too if need be (or, if possible, I could always return fish as well as my priority is to upgrade my Bettas).
It's looking as though now it's just deciding what and with who. I do have numbers figured out already (using AqAdvisor), so if I go with any of these, this is how many I would get in combination with just a Betta and/or shrimp: 8 Harlequins, 10 Mosquitos, 10 Galaxies/CPDs, 4 Peppered Cories, 5 Kuhli Loaches.
Any other input is very much appreciated, however! The more I know the better as far as I'm concerned.