I ended up getting T5 belts and T2.5 aluminum pulleys and I am waiting for them to arrive. Certainly, I worry less about cracking those pulleys as the most I am likely to do to them is ream out the bore to fit my stepper shaft. I think that your resolution is as much guided by belt and pulley as the stepper increment. If I vary the diameter of the pulley, I can change the travel amount (small step, larger travel in bigger pulleys). After thinking about it, all things being constant, I don't think the number of teeth matter. What I think an increase in 'teeth' will give you is better control of the belt, assuming there is no slack in the belt and the teeth in the belt and pulley match exactly.
My preference really is to use a screw cog assembly, much as you have in the vertical axis of the printer. I can control the travel by changing the pitch of the threaded rod. I saw, on Thingiverse, someone who devised a linear gear that you bolt onto the table and the number of teeth there and on the drive gear control the travel in that horizontal plane. I like that because there is no need to worry about slack and belt wear. Something to consider if you are planning an upgrade, and maybe even offer as an 'upgrade'.