1): You can totally get the mechanical RPM without hall sensors, as it is always directly proportional to the ERPM. ERPM can be estimated from BEMF Zero-crossings, and other methods.
Just multiply your desired mechanical RPM by the number of pole pairs of you motor (7 in your case) and you will get the ERPM to send to the VESC.
2): Assuming all other settings are correct (battery current limits, etc.) the VESC will also apply negative torque ("brake") in order to keep the set rpm.
This is, of course, limited by factors such as motor torque, max battery current, etc.
Remember that regenerative braking feeds back energy to your battery. Two things to consider:
- Set your max battery voltage to the max voltage of the battery
- Braking will not work if the battery is full (have not tested this yet, but I assume...)
Long story short: the integrated RPM Control is exactly what you need