Yes, that would do it. 12/48 would probably be sufficient for that, actually. Just swap the sprocket and see how you like it, since sprockets are cheap.
Flywheel weights can be handy for putting around in tight stuff, worth a try I'm sure.
Threads in the middle of the flywheel? no it doesnt,it just goes on a tapper. there are threads on the middle of the shaft though,thats were the bolt goes