If you want belt drive, first thing is to look for frames that can take belt drives. You need a rear triangle that opens up. That should give you a width that works with suitable hubs ”automatically”.
Not aware of too many SS belt drives. Might be simpler to buy a geared hub and just not shift it.
Don’t get hung up on tooth counts, it’s the ratio that’s important. Any sets of two numbers that when divided give the same result will ride the same. With that said, 55/17 sound high on a bike with regular wheel size.