It's always great to encounter an intelligent, hardworking person who's decided to mod Morrowind.
I currently have...well...
170+ mods running, and new factions are in high demand. Note, though, they are probably the hardest thing to create. You not only have to build your own faction, but somehow see that it fits seamlessly in with the others in Morrowind lore, and that the code doesn't step on anything else, in the process. There are some good faction mods out there; you might want to check 'em out for examples.
My suggestions, for what they're worth:
1) Keep your mod tightly limited, and focused. I have literally witnessed more than 100 mods that expanded rapidly into claims for all sorts of things, then imploded. This isn't a criticism, it's simply a suggestion.
2) Concentrate on error catching--not in the code, but in the player's actions. The player might find a solution to a quest which is not the one you intend in some detail, and the mod would then no longer recognize the validity of their success. This has happened a lot of times in quest mods I've played, even the better ones.
3) Concerning the Centaurs: the animation alone is going to take a lot of time. And how will you handle clothing and armor? There are hundreds of armor mods, dozens that are popular, plus all the standard armor. Will you make new meshes for them? Unless, of course, they're only called centaurs, and not real centaurs. But in that case, why call 'em that, and lead to confusion with players looking for downloads?
4) Harder skill requirements for all factions: already done. Superadventurers, an excellent mod, is probably the best known that mods this, though there are several others. You can save yourself some time, and simply make your own faction hard to advance in. You might also suggest one of the faction requirement mods as a complement to yours, in the readme. Anyway, just a thought.
5) Less errant missions, more information-gaining missions: I assume this has to do with your quests, and I like it a lot. Some of the mage faction quests are like this, and they seem more realistic when well chosen then the inevitable FeDX quests.
6) If you're going to create a giant floating fortress as a stronghold, you have to think to yourself: hmmm, why didn't the Telvanni come up with it, first? After all, they're heavily into magic, they love putting things out of reach of non-magical mundanes, and they're all for arrogantly large buildings in keeping with their natures.
So, for what little my opinion's worth, I think this runs against the accepted frame of Vvardenfell reality,as we know it. Still, in the end, it's up to you.
Good luck!
