The re-entry is the hard part! Ha ha, a stainless steel ladder is definitely a must. You would want to bracket the ladder to accommodate heavy loads.
You also need a boat size dive flag and a means to fly it.
02 would be important considering your distance from shore and traditional EMS. In terms of First Aid I would also assemble procedures for those serving topside duty while you are diving. (Don't know your buddy situation or diving preferences). Mine include how to retrieve a diver adrift, calling the USCG, GPS coordinates for each dive site, starting the engines and getting underway, retrieving the anchor, etc.
Definitely need a way to keep tanks and gear secure while underway. It's more convenient in terms of space use to stow your tanks upright. I will be adding a series of SS rings along the gunwale.