How many paddles?

You'll love the paddle in the sand dunes, it handles fine out there as long as you stay on the gas. The hookup is amazing.
Most guys I know run 8 paddles even on their 500's. Some run 10's but it bogs the motor more and requires more clutch/shifting work for just riding the dunes in general because it allows virtually no wheelspin.
My suggestion is:
Hillshooting with a powerful bike (250 or 500): 10 paddle.
General duning (250): 8 paddle.
125 or 80's: 6 paddle.
I usually ride at Little Sahara.

I have run the Skat-Trak hooker and the much cheaper Cheng Shin and I like the Cheng Shin better. A lot of guys around here also run Turbo Paddle. Turbo paddles I think are made by King's Tire.

D756 would be an excellent front tire. I had a 752 on my KX and it did pretty good on the sand. I have a 739 on my YZ and it is OK but not as good as a 752 or 756.

I really like the Cheng Shin, that's what I'm running right now. I have the regular (not the Sand Pro) that has a little shorter paddles, but I am running the 10 paddle.

Are you planning on the 8 or 10 paddle?

Sand mountain really isn't bad at all with a paddle. You'll be making those quad guys feel really bad in the drags in no time at all!!! :)