We do charters on this boat 3 times a year, plus one on Truth Aquatics smaller boat the Truth. I'm assuming you will be going south, as that's typically what you do on 4 day trips. All the advice listed above is good.
We usually bring our own bedding materials, ie sleeping bag. As for gear, sometimes it can be crowded in the storage areas on the deck. Bring a mesh dive bag to store stuff that you will need on each dive. If you have a large dive bag or plastic tub, stow this down below the wetsuit room or some where out of the way to save space. I'll attach a checklist that we send out to people who come on our trips.
One really nice thing about the Vision now is that they changed to new engines earlier this year so it is a whole lot quieter in the bunk room. I would also request a double top bunk if you can.
Dan