How to create the evil overlord race?

What I would like to do is to create a single race (non-player) in a game which is much st´ronger than all the other races. Something like the Antarens in MOO3. To this purpose, the race should have much better tech than the other races. Ideally, the tech difference should exist from the outset. ALternatively, the race should initially have much better research capacities than the other races.

To counterbalance this, I would like to minimize its growth, so the evil overlord race would be severely hampered in its expansion. It would be strong in the beginning but as the other races expand (if they are not eliminated by the evil overlord) they catch up and finally overtake the baddies.

Can this be done? More specifically:
-How do I give one race a massive research advantage or even better much higher starting techs than the other races? Can I give them tech löevels from the start? Can I give the homeworld facilities which the other races do not have?
- If I reduce growth, will this be sufficent or do I also have to adjust migration?
- How do I stop the evil overlord from over-expanding, i.e. colonizing many worlds which they are afterwards not able to develop due to their growth constraints. OTOH, I want them to be aggressive within a larger area around their homeworld, even if they cannot really colonize the whole area.