[Andrés]

There's no problem in having multiple prop types. Unless someone "cheats" when selecting racial traits, you'll never see b5 engines in trek hulls.
I admit I'm tempted to abandon q-n movs for the sw ships in order to be able to restrict standard movements more easily.

I like your idea of common tech trees and I admit I had thought about it and discarded it as too complicated (what means that I was too lazy to implement it at that time)
But I’d go for a mixed system, it works nicely for “ship construction”, but I’m not sure about beam weapons, it’d sound strange to research “Energy Stream Weapons” to get phasers, disruptors or turbolasers.