On dive site recommendations... Kona is nice in that it has lots of good dive sites, and beyond the night manta dive there really isn't any one or two dives that stand out as a top knotch dive site to the exclusivity of the next best 10-15 dive sites or so. I would not sweat worrying about what dive site to visit as all the operators here pretty much try to show you the best dive sites available on any given day - a lot of it will depend on whether or not there are ocean swells at the time (conditions can change day to day in the winter, so site selection can also change day to day) and which direction they are coming in from.
If this is dive number 7 for you, unless the first 6 were in Fiji or other equally nice South Pacific/Indian Ocean or Red Sea dive spots, you should be favorably impressed by everything you'll see here.
Have fun.