What if for the time being, you simply make the units as a normal progression. In other words, make some of the later techs (weapon, armor, and reactor) dependant upon earlier ones, so that you can obsolete units instead of making many permutations. You can cut many of the in-between stages out as well as items like unarmored, heavily armed needlejets. Also make the special abilities promotions using the standard XP system. This will vastly cut down the amount of models you need to produce, and while it will offer fewer options than you may like, it will enable you to get an initial release out. After that, you can worry about adding in more specialized units.
Your focus for now, in my opinion, should be the following:
1) Basic terrain and improvments
2) City and static leaderhead designs for Vanilla factions
3) Tech tree
4) Basic selection of Alpha Centauri units with basic promotions
5) Civics and possibly religions (Centauri, Humanism, Theism)
After that, you should be ready for a release. Through the release, you gain further support and assistance. You then begin to add in and/or tweak the features you want, things like Alien Crossfire factions, more units, new game features, etc.
Seriously, your work so far looks amazing. I loved SMAC, and would love to see it brought over to CivIV. The fact that so many groups have started and stopped is sad, but I'm glad to see it picked up again and hopefully able to build on the resources of the past attempts. Maybe we'll actually see a release this time around.