Yes, you can sleep on the Great Escape. Any trip, the night before.
Crew will be there to have you sign all the paperwork and show your C-card, sign-in for your bunk, and you are set. Lots of people do it. You are allowed to start loading your stuff on the boat the night before around 8pm, or whenever the crew shows up and starts prepping the boat. We always sleep onboard as we drive in from out-of-state. There are lots of others who also sleep onboard who don't live in the area. Also, if you sleep onboard, you can set up your gear the night before and get a good spot.... those people arriving in the am are all half asleep and cranky, trying to schlepp dive gear from their cars and find an empty spot to put their tanks, etc.
If you really want a guide, you need to e-mail Tim and request one. I am sure he can find you someone to dive with you. But as mentioned before, you probably don't need one. The Catalina dives are always pretty easy and relaxing, just make sure you and buddy know how to use a compass to get back to boat. You won't be able to see it until you are very close, but you can listen for motor to help you know you are getting closer.
A few things you need to remember.... if you get caught in the kelp - freeze! Don't thrash around. Slowly try to located where you are hung up, if you can untangle alone go for it or let your buddy do it. Kelp is east to snap in half if needed.
Also... you MUST bring your own tanks and wts onboard. They don't have any onboard.
You also need a 7mm suit, one piece or two piece, and a hood and gloves. Water is cold and after a couple of dives it seems even colder. Bring dry clothes to change into after you dives, the ride back to mainland after diving is about 2 hours, plenty of time to catch a nap downstairs.
Also, you cannot go downstairs wet, no wetsuits, so you ask a crew member to get something out of your bunk if you need it. Otherwise, bring everything upstairs (like topside camera, logbook, sunscreen, hats, towels) and store them on one of the shelves in galley for easy access, or bring a dry bag to stow under your seat or with your dive bag stowed on sides of the boat in walkways.
You can bring your own small cooler onboard if you want beer or some special drinks other than sodas. (They have some beer onboard but it is extra $.)
See my photos of the boat here:
California on the Great Escape - August 2008
California Kelp 2007
robin