to first q, not sure about your shifter - brake cutoffs can be inline mechanical or hydraulics with magnets which are a bit more finicky. newer kits with torque sensing motors you dont really need brake cutoffs. recommend a cyc photon due to this. 2nd question - because the motors chainring replaces the front derailleur grears to do all the work for us, and adds a throttle/display.
This is probably a stupid question. But why do we discard the crank gears and front derailer when we convert to a mid drive motor?