UCF your on the right track,
1 you have picked the 12'6'' which is bigger flotation and not much more weight than a 10', which will help balance weight of dive gear.
2 your in florida and have small weight belts, a big plus.
3 a 15 hp is a 10 hp just a different carb on most makes.
4 A dolphin hooks to the cavitation plate on your ten hp that lifts the back up to plane, with an attached to back of transom plate does this also and you can use both. This has better fuel economy also.
5 AL anchor, and unless needed gas use a small fuel tank. when going far, the fuel will be less weight on the way back.
I now use a 5 hp 2 stroke merc on a 12'6" zodiac MkII C GT, with a dolphin on motor and a 3 1/2 gal tank. the tunes are bigger than others this size. I use 22# weight belt, and I get on a plane and cruise pretty good. I get on side of toons to drain water from suit and I drain water from bc before getting and putting in boat.
I have a 25 for it also and it is if I need for another diver, but I have a big RIB zodiac for that.
The lighter the motor the more you like dealing with it.
You will learn how to make it work and it is very easy on the pocket book per dive.
My 5 hp set up is like $.35 a dive of three mile trip about.
I also use a tiller ext, and have a rope in front I hang on to when surf is up and stand up for less weight on toons.
Have fun as it is fun just to go diving as it is diving.