I've thought about a speed reducer and/or a servo. I'm practicing and getting control of it with the full blast clutch motor. I stitched a practice strap, .120" thick x 1/2", one line down both sides, today. I had one spot where I wandered.
This is strictly recreational for me, so I'd like to avoid throwing another couple/few hundred dollars at it.
I did caliper the shaft and pulley bore. Right at a 1/2".
The motor has a 2" pulley already. I've used that pulley calculator site many times. My 3" hand wheel pulley against my 2" motor pulley gives me a max of 1167 RPMs (1750 rpm motor), which I seem able to run at about 1/2 speed by feathering the clutch. With thinner leather or thick denim, I can feather a stitch or two at a time as-is. If I can get an 8" pulley on there instead of the roughly 3" one, I think it'll slow down enough to serve my current needs.