I wouldn't recommend drilling trough the output shaft of a drill. Seen it before, and it will give a nice weak point that will snap.

On brushless drives. 350W/7.4V= 50 amps. 50amp esc's needed...

But I think it will work nicely. After all, Hannibalito3.2 drives on 3S with 28mm diameter unsensored brushless motors.