I have a project that will go in the water this summer. I am collecting parts to get it together. I have a Bravo 1 drive with 1:50 gears, 24' Warlock Euro (about 6.5' wide) w/ 25deg dead rise, 468 making +/- 450hp, hull weighs about 2700lbs, fully dressed 4500lbs +/-

What prop should I start with? Dia & pitch???

If your x is low ie. 15" or less, I'd run a Mirage+ 25", a Rev4 25" as a 4 blade alternative, especially if your x is 16"-16½"+. As out of the box props goes, I'd say the M+ and Rev4 are better choices than the B1, but testing a B1 and have that labbed is of course an alternative too. If you choose to do so, I'd start with a 26" and in this case, contact Bblades. When you have as many unknowns as you have, you will need to dial it in. This is if your motor is making power around 5000+ rpms.