The 48 will fit fine. Water I believe is $.20/gallon and is metered. Make sure you look at the meter reading right after arriving. Last time I was there I got charged for way more water than what I used. Trash I believe was $5/bag so make sure you've got a big bag. You will be stern in with the spring line on the finger dock. Unless you have plenty of slip experience I would recommend getting there a little bit early in hope that you will be the first boat into the slip. All of the slips are wide enough for two monohulls. I find it a little hairy squeezing into the slip with another boat already there and the wind blowing at a good clip. I obviously need more practice!

Besides the cost you mention you will also get charged a per head resort fee. I don't recall how much that was (I was there August this year).

There is a free ferry to Trellis. And I agree with you that Scrub is a nice place to pick up some guests. You don't need to go pick them up. They'll arrive whenever they arrive. You should check with the front desk to get the ferry schedule.

I much prefer the outdoor restaurant so I'm glad to hear it's back open (it was closed in August). The food there is fine. And fact I think the best cheeseburger including fried egg anywhere in the islands.

The grocery in the best of times has been marginal. Some drinks and some canned stuff. Maybe a box of cereal or two. You are way better off running your dingy in to Trellis.

Booking is an interesting question. My experience is that it doesn't matter and that it's first come first served. I'm not positive about this but this has been my experience. The times I've made a booking they can't seem to find it nor did they seem to care.