What's the consensus 1 or 2pc? for Wheels and the Tamiya HMMWV driver lower half?

Hmmm, depends on how many you want. I made a 'peel' back one piece mold for some wheels once.
I poured a one piece mold and carefully cut a line evenly down the lengthwise middle of the mold. This let me peel back the top to ease the wheel out.
This is easier to make a mold, but the mold doesn't last long.
If you want to use the mold for a lot of wheel - I'd go two piece.

this one i'm only figuring 8-16pcs (minimum) for the wheel.... not sure what to do for the Seated figgy half.....

I poured a one piece mold for my wheel and tires. After it set up I cut the mold in half along the center of the tread line. I have made at least 100 or more tires from the same molds. These molds are over a year old. I found the secret of using baby powder as the releasing agent instead of using a petroleum based product. The powder will not attack the rubber mold and it makes the clean up of the parts a lot easier for painting. Our good friend Joe Wallace told me about this and I have been using it ever since.

As far as the lower body part of the figure I would use a two part mold. I think that you will get a much cleaner and crisper looking piece.

Dave

Matt all the wheels/rims I have done are one piece molds and I have had no problems with them.

cheers
Cliff

! pc it is for the wheels..... thinking i might cut the lower half of the fig. in half too.... might be easier to mold.....