I can’t speak a lot to the differences between the Grom and Z125. I watched a few videos and they perform very similarly. I think the Grom has a much larger after market. Michael can give you lots of info on this.
For Street, I don’t believe there is a CRF 125 dual sport available. Dirt/trail only. You would have to stick with the Grom/Z125.
For Mini Racing, the CRF125, Grom, and Z125 are legal for the Stock 100/125 and Stock 100/125 40+ classes. However, very limited mods are permitted. Stock exhaust. Stock motor. Stock suspension but you can upgrade internals and springs. Wheels and controls can be changed.