1. depending on your characters godly parent will determin the cabin that they stay in. If you have a son of Apollo, he wouldn't stay in the Hera cabin, it'd be the Apollo cabin. But, if your character is unclaimed, then they still stay in the Hermes cabin.
2. You can RP in any of the locations(excepts places like the battlefield, and others like the underworld or the labrynth you need to ask a admin before posting in)
Example of an RP(i'm using my own characters.
It was around 5 or 6 when I woke up this morning, so I headed down to the beach. It was nice and quiet, listing to the sound of the waves. I lied down on the sand, and Dawn sat next to me. Suddenly, I heard someone come up from behind.
Notice how I make it so that way the person who reply's has a place to start from. When you do reply, you wound't say something like...
I was finished my morning jog, and decided to head to the beach. It was a nice, quiet place, and I was all alone
as you can see, these two RP's have nothing to do with each other except the fact that there both on the beach.
I hope that awnsers your questions!! If you also want better RP examples, click all of the RP locations and read some of them.