frankly the only way to do this "well" would be to come up with a bunch of mech designs for each in-game faction and give them all a set of mechs
the only feasable approach is take the ships of thoses factions, hackem up into bits and make mechs out of them, no need spriting from scratch if it ain't needed, plus it would probably help thoses mechs fit into the faction a little better
all that it would require is one base per ship tonnage and then roll out variants of theses like what battletech does
Heck a mech version of the Hound could be interresting, arm mounted assault chaingun and a vulcan for a head, thats a pretty decent mech basis
Same could be said of the ships of the same kind, Keeping the weapons loadout and switching around the weapons arcs would freshen them up a nice bit