I have been on this trip. I did not do the extended land portion, but instead flew into Santa Clara, (Cheap flight on Southwest out of Ft. Lauderdale) and the Aggressor folks picked you up at the airport. The bus ride is lengthy but interesting. A guide is on the bus and is more than willing to discuss things regarding Cuba. You do get to see a bit of the country side, which is pretty informative regarding how the folks in Cuba now live.
I would not worry to much regarding changing currency, you can exchange a small amount right at the airport at the Government exchange location. Little outdoor bar at the airport where you can buy a cold beer for $1 or 2.
The crew on the boat is very attentive. It is diving from tenders so get ready for a couple of bouncy rides, but nothing terrible. Food is very plentiful on board, Cuban coffee is strong and lots of fruit.
Diving is mostly reef style in the 40 to 75 foot depth range. Reefs are ok, fish are fairly abundant in some locations.
The harbor where you get on the boat is locked up pretty tight, you are not allowed to get off the boat once you are on it.
Any specific questions?????