[deep thinker]

For yourself as a diver, a rubber weight belt with quick release buckle and the apropriate amount of weight to make you neutral at say 5 to 10m depending on how deep you plan to dive. Speargun wise Id say go for a 1m to 1.2m gun depending on viz in your area you plan to dive and for a strong gun with good performance on bigger fish Id say go for a Rob Allan or Rabitech, but that depends on what is available in your area and how much you plan to spend. Please also note that this is a very broad reply to your question regarding diving gear if you give more details wed be able to give more accurate replys.
Boat wise Id reckon youll need the following, first of all a skippers license and the necessary safety equipment like fire extinguishers, life jackets, flares and a two way radio wich should possibly be the most basic needs to get your boat certified as seaworthy and how far you can go out, but check with local legislation about exactly what you need. Also youll need a GPS and a echo or depth sounder that can pick up fish and depth below the surface so that you dont spend all day diving in a area looking for fish or all day riding around looking for a place to dive. Another nice to have is a speargun mount and hatches where gear can be stored out of the way. O and a alpha flag for when you have divers in the water.
Hope that helps...