[GulfCoastAquarian]

Your assumption in question number 2 is exactly correct. The 4x ODNO F32T8 bulb consumes only 80 watts, but produces 6500 lumens. The standard convention of "watts per gallon" comes from a 2000 lumen, 40 watt standard F40T12 bulb. This ODNO F32T8 bulb is far more efficient, so it produces as much light as 125 watts of standard lighting (like three 40 watt tubes).

As for your first question, T12 lamps are 1 1/2" in diameter and T8 lamps are 1" in diameter. Each number in the T# convention equals 1/8".
A T8 and T12 bulb has the same pin configuration, though, so you could use T8 bulbs in the same sockets/strip lights that T12 are used. But if you want to use GE Plant & Aquarium bulbs (I love 'em!) then go on and use them. They won't be as efficient as T8 bulbs, meaning they'll need more watts to produce the same lumens, but should still produce about the same light. The ballast should just work harder.

I'm going to be testing this theory soon. I'm going to find a 4-F32T8 ballast and try various configurations with my two 40watt GE P&A bulbs. (One bulb with 2x and 4x, then Two bulbs with 2x each)