"geared" crank mechanisms
I was wondering if anybody has had any experience with attempting to build a geared (spur gear) type mechanism into the crankshaft to obtain the rpm's required for the bellows with fewer revolutions at the crank. I have built a midi organ that does not have any assembly for roll music. I am guessing that the trade off would be a harder to crank organ. What about a flywheel??

If you have built your bellows to more-or-less traditional measurements for hand cranked organs, the cranking speed will be about right - somewhere about 60 rpm. (Note that rpm may not be an EU approved SI unit, although it is commonly used. Engineering calculations tend to be based on radians per second.) Generally the "gearing" is to reduce the speed of motion of the cylinder surface or card or paper. If you built to a completely original design, then other's experience may be on little use.

You don’t say how big your bellows are, but I have powered my bellows on my 65 keyless midi organ with a car windscreen wiper motor. This give a nice cranking speed of about 65 rpm, you also have the option to run it slower if it is a two speed motor. I have fitted a switch to my reservoir so it runs on slow when not playing and switches to fast when the air level in the reservoir drops. :D

geared cranks
I have considered the spur gear option, i think in light of slowing the crank revolutions, it would still require extra force to get the same amount of work done. I like the idea of a flywheel, but which would be better... a circular type on the shaft or an extended weight opposidte of the crank handle. I am looking at an ametek blower and separate 12 v motor so it can run it during breaks.