Clifford... with regards to being best friends, I am easily bribed with offers of free high quality SCUBA diving!! LOL!.. thanks for the props on our websites. I appreciate it.
Your basic construction that you've outlined sounds like it is a reasonable plan. Some thoughts:
Control Room: The dimensions of this rooms are critical in determining the even distribution of low frequency modes... This is why a rectangular shape can be easier to work with than odd shaped rooms. Also, thing symmetrical!! The front half (at least) should really be symmetrical to make your monitoring environment best as possible. If you do a little digging you can find a number of resources (Ethan's site, RPG, etc.) that can help you calculate the modal response of a rectangular room. This is where I would start. It's not too late, as you havne't built any interior (or exterior!!) walls yet...
Detailing for windows and door penetrations can be finicky and are very important in determining your isolation between rooms.
Treatments>>> THere are many posts in this forum about basic approach to control room treatments, BUT you have to start out with good acoustic proportions to have any chance of getting smooth bass response!! This is the single most important starting point and can be almost impossible to 'fix' if it's messed up at the beginning...
Electrical: sounds like you're making a good start of it. You might want to consider an isolation transformer between your main power feed and the sub-panel for the studio power. Segregating the power as much as possible, as you've outlined, is good... and the physical separation between audio wiring and high voltage AC is also important.. but, even with a separate ground the actual hot legs for the power still come from the same source... Not sure if Nassau uses 220V 50Hz or 110V... if your electrical power uses a Neutral connection, there can be much noise shared between your house and studio via the neutral. An isolation transformer will provide you a completely separate ground (connection for your new ground rods, etc) and a clean neutral or two clean hot legs to base your studio power on. Oversizing the wiring as you've mentioned is also a very good idea... Lower resistance = less voltage drop = less potential on the ground (or neutral)...
Think about how to best implement your (rectangular) control room... look at the modal response based on all three room dimensions, then layout the rest of the rooms based on the best control room configuration... This is how we do it for the big boys *simplified of course...
Stay in touch and let me know when you're sending me a plane ticket so we can do some diving... and possible talk about studios a little too!!