welcome to the huntsman club!
Good luck on the build, it would be great to get a load of these boats together! (Martin are you reading??)
just a few points that might help you save time and money, your boats is the same as mine, its a Veron design, little bit rarer than the Precedent design, and slightly different. Remember that all the plans kicking around where based on ic engines, hence the very different prop angle, you last pic looks good, try and get the shaft as flat to the hull as possible, then the prop is pushing the boat forward, and not upwards!
Regarding the prop size, they are approx £1.50 each, get a couple, or borrow as I did! start small and work up after short runs, testing the temp of the motor, make sure you have a fuse inline to protect the esc, If memory serves me right those supermarine mtroniks where quite expensive, I think they are capable of running twin motors, just a pity the max volts you can use with it is 12volts, that kind of limits you, as the graupner 700's nominal voltage is up to 14, and upping the volts makes a huge difference to performance, those motors love big volts, and that hull thrives on speed, they handle beautifuilly.
I did the same to my side windows and screen and removed them, some early 28's where like that. My first set up was with a700 bb turbo on direct drive, it gave pleasing performance, its not rocket fast, but very acceptable, try and trade the battery pack for two 6v sticks and wire for 12v, then each stick can sit either side of the motor low in the hull to balance the boat, and if you manage to get a higher volts esc in the future you can just add another 6v stick to go to 18v, and so on