RTF is a global modification that replaces all towns in the game.

Yes, the first option would be the best, but let's make the access to the super-elite and super-basic units available later than the standard ones.

Okay. Maybe we can make it so that building a super-basic unit requires two regular basic units? Or is such a strict requirement unnecessary, and it would be better to simply increase the required city level?

Added 3 minutes later
And here's another idea: can we create a building that only improves a specific unit?