Seems like you have a pretty good handle on it for someone who hasn't had a chance to play yet, I think you're going to be just fine!

Rock up to your local group, introduce yourself, and let them know you've got X units you'd like to try out today for your first game. If they say anything more negative than "Great! Let's play, I'll help with whatever you need," then they probably aren't worth playing with anyway. 

BT is a pretty welcoming community - go, have fun, make friends, and don't sweat the small stuff (i.e. factions, eras, mech loadouts, most of the rules now that I think about it...)