Hi Lulu,
1) It does depend on the hotel, if there's a mini fridge just buy a few water bottles yourself and store them in there for clients. I wouldn't worry about feeding them, if they want to eat they can take you out, or wait until after their session.
2) ...I've really no idea how you can do this other than just asking and playing it straight. Claim a big spillage? Otherwise I'd be prepared to bring several from home.
3) Bounce up and down, jump about, move. Nervousness makes you restless, and this has the added benefit of making you sound breathless (hint of what could come?). Write yourself a little script, and read from it, write down their answers so you know what they want.
I started a long time ago doing phone sex, practice dropping your voice slightly, nerves can raise the pitch quite a bit. Create a persona, keep them talking about themselves and what they want, the less air you have to fill. But don't let them wander into a fantasy, keep them to the point.
4) If you haven't got one, get a douche, use it till you run clean. Just use the hotel bathroom before they arrive. Get yourself some good lube, I use YesButt, Silk is also good. Don't double dip, change condoms between holes. Don't eat anything spicy. Start with you on top, control the depth and pace for the initial penetration.
If it's too big, you can always say no. Play it off like a compliment. "Gosh, I just don't think I can take that, you're so big. Let's try some other things first."
If you're not used to doing anal, get some butt plugs and try wearing them for a little while, working your way up. Can also be quite a thrill for clients to discover you wearing one when they go for a grope.
Just breathe, have fun, and remember, don't push yourself to do something you're not comfortable with.