Round Valley at 8am on Sat? You need to bring your OW cert - anyone will do, a license and I think it is $10 for NJ resident - $20 for out of state and you need to check in / check out at the ranger station (right before you enter the park is the ranger station).
Do you have a preference of just putting around or do you want to go find the sunken town? Not much deeper than 25 or 30 feet but it is a hike to get there - usually walk in the water to help with the weight of the gear...
Bring 2 tanks or 1? The first dive if we go find the town may wear you out - if not I might be game for a second tank dive...