If I recall there's about 80-90 tech slots and around 50-55 unit slots. There's 3 extras of each, plus the original slots.
There are special qualities to some of the slots, so you should read up on those (available elsewhere) - but you CANNOT create new slots.
Oh, and you can't do anything with the future techs. It's just what the game tosses at you when you run out of techs to research.