Luca: He's lavish with his friends because how else has he ever learned to express affection? Might just depend on catching them both off-guard to see how they get along in the end. His fight for emancipation was not secret at all, since his fight with his folks originally occurred after his grandmother died during freshman year. He figured since everyone heard about the first parts when they happened, no point in trying to keep anything else secret. He's a pretty open guy in that respect.
Penny: TJ is a city boy through and through (I'd love to see someone drag him camping *laughs*) but yes, very very friendly and open. TJs good with being friends with Penny. And thinks she's pretty cute too, but so not admitting that Out Loud.
Gatsby: Friendly, sure! TJ's got no issues with his own sexuality, so he's not going to be threatened by Gatsby being the friendly sort. Party, so very definitely. Plenty of crash space, food, drinks, whatever's needed. And the servants have the night off so it's just TJ and schoolmates in the apartment.