If you ride mountain trails, a front hub will be an horrible handling nuisance. And, your small battery will have a very short range powering both motors.
The best solution is to build with a faster, more powerful BB drive, or to trick yours as some had succeeded making it much faster.
The 2nd motor solution must be on the rear in order to make it a good ride.
In all cases, you will need a bigger battery to achieve your goal.
You can 'mountain bike' with a front hub motor, but yes it's pretty annoying downhill. If it's just casual it will be fine. Just remember that it's going to understeer. The handling is actually not that bad, it's the understeer that is really bad, the wheel just does not want to turn correctly in dirt over about 8-10 mph downhill. The same reason why the older 90's front-drive cars can't do a racetrack, they are just fine on the street but not a real track.