PCB is pretty packed right now and will be through the end of July. You'll definitley meet more than 3 people!

Holiday Inn is a great choice. So is Boardwalk, Chateau and Edgewater.

As for underage drinking, you'll have to use your own judgement on that. Clubs will still be fairly strict. The beach is more relaxed. Unless you're causing trouble, local law enforcement will usually leave you alone. Just DON'T drink and drive.