Glenn, what size of rear tire are you going to use? I would put enough tire in there so you don't have to put biggers tires on later.
Also, if using a treaded soft compound tire, my tires grow about 2.5" in height under power.
Give yourself lots of fender to tire clearance, at least 1.5", I notice a lot of people have their fenders almost touching the tires to get the seat lower in other classes, that is no longer an issue on these machines.
As far as the seat location goes, the seat will look a lot lower when the fenders are raised up.
7-7.5" from the bottom of the seat to the ground is about right, I actually ended up raising my seat up to make my machine work.