You might get away with deep groove bearings for the spindle nose, however they're not ideal as they don't handle sideways loads well (i.e. plunging/drilling). Ideally you need angular contact bearings mounted back to back with some form of adjustment as they'll handle all the usual cutting forces, and allow you to adjust out any movement.

The purpose of the top bearing is to support the shaft. Provided the motor bearings are good enough, then you don't really need it. I've got no experience of outrunner motors, so I can't say if they'll be good enough or not.