mine are direct drives but if i had the choice i would go for belt drive for the reasons you mentioned plus you can upgrade to a stronger machine by changing motor size only.
larger wheels are available through most industrial polishing supplier
(sent you a pm about that)
10 inch wheels with a 1750 rpm buffer can get you a very good result with less material wasted then with a 3450 rpm 10 inch wheel .and at the same time running at 1750 with a 10 inch wheel makes it a safer speed and less chances of damaging some fragile parts.
