As far as ID questions, you may want to check out the California Department of Motor Vehicles for ID. They issue CDL's and simply Identification cards. Using a motel address may not be the best route, you will need to phone or maybe email them. Let them know you just moved here (even if just visiting) or tell them you are moving and contact now? Either way, you will get answers there. You wouldn't want to put in for a Driver's License unless, willing to give up your current state's DL.

You can get a Post Office Box and they request, I am a bit fuzzy but minimum things like, mail sent to your at the address you post as your current addresss (motel's addy) and I am thinking a State legal ID. You submit and once you meet all the Post Office's Demands (I'd call ahead to find out specifically they request. Good Luck to you! pr