With 10" wheels you could use a standard motor without gear reduction that has an 11 tooth sprocket and an 80 tooth wheel sprocket attached to a freewheel. Here is the calculation for this setup.
We currently do not carry brake levers with parking brakes but they are available at many bicycle parts stores. We do plan to carry them in the near future though.
Please let me know if you have any further questions.
The freewheel could be locked by welding its stationary and freewheeling parts together, but this would not work because the freewheel is threaded onto the rim and if it was used in reverse it would unthread from the rim and no longer be attached.
A sprocket that bolts directly onto the rim would need to be used for a scooter that has reverse. Here is an example of a rim and sprocket that bolt directly to each other.