IMHO, You can use any wheel that you can make fit, the diameter of the wheel should be as close to original as possible to aid in blade alignment, the bore of your new wheel needs needs to match the axle that it turns on you might sleeve an oversized bore to fit on a smaller shaft, or change the bearing size for your situation.
AFAIK, Spokes serve to lighten the wheel. I have seen home built band saws with out spokes and wooden wheels. the wheel width needs to accommodate the widest blade you will be using.
Home Built Band Saw Mills sometimes use car tires and rims as wheels; either the Lower or Upper wheel will be powered, sometimes by a engine that drives the Upper Wheel as the carriage passes the log being sawed into boards.
