I'm finally not the one doing really long posts to discuss things with the GM!

What happened? Did the "precursor civilization" mentioned in the OP systematically murder most of the other races?
Would it be alright if I play as an interstellar megacorp?
Basically I'd less of a civilization and more like a corporation of great number of companies that are present in at least hundreds of different civilizations.
I may be the largest shareholder in these corporations but my holdings would be subject to the local laws in general.
I'd only own a single planet which would be also the megacorp's headquarters.
As for tech it'd be technically a mish-mash of anything which can be traded for in the galaxy along with the company's own researches and improvements.
So yeah, basically a galaxy-wide megacorp which would trade with nearly anyone else.
Capitalism at its purest.
(You can't hug a person online... YET)