If my party is at 6, can I arrive early to set up?

Yes

I have scheduled several parties there and was allowed to get in early and set up each time.

Agreed. Call and ask first, they usually allow about 30 min early. There was only once they had booked back to back parties and we couldnt set up early

Yes definitely... I had a party there and they let me set up.. up to an half hour early

I would imagine that you could. Call just to make sure.

Best to call and ask the front desk