Good matchups for beginner?

The Korx are a good pick; they won't go all WAAAAAARRRRRR on you, since they are mostly traders; but if you pick a  diffrent alignement they JUST might attack;  Granted, the only time they declare war on me (I play Terran), they claimed someone paid they a good chunk of creds to get in trouble with us.

Or get a military race (Taurians are ok) and maybe have the Altarians in your team to back you up: they research, you bombard.

Iconians are good if you want a lot of techs(just make sure you have money)And allying with the terran alliance is good too.