I'll throw in a few cents too;
2) If you attend in September you don't need any kind of cold clothing. You wouldn't anyway, just for living here in SoCal, but some of your cross country flying might take you over more mountainous terrain, and I would pack a few pieces of warm clothing for that, in the unfortunate event of a forced landing or some such.
3) Don't know what they're like, haven't been to them. According to my students they're not too bad, there's a pool at least. They're only about a 4 minute drive from the airport.
4) As you say, those days will be rare, but in the event you should get a day or two off, I'm sure you could find something to do. Go to the beach, Disneyland, Sea World in San Diego, Universal Studios in Hollywood, countless museums, so on and so forth. And it's not like there's nowhere to go if you feel like being social in the evening.
5) No, normally someone from somewhere else who also went through the program alone will be paired up with you.
6) As aloft pointed out, ATP has it's dispatchers in the main office. We do have a good relationship with them though, all the instructors know them personally, and if you don't throw any temper tandrums during your cross country flying you'll have a good relationship with them too.
Hope this helps.
Cheers,
Helge