I have found that hand files work the best. I tried quite a few attachments to my dremel and a mini hacksaw, but nothing works as quickly or smoothly as a file. You can draw lines where you want to file down to with a fine point sharpie for some guidance.

As far as balance, that tends to be a personal preference in this forum. Some say the weight is too close to the axis of rotation to make much of a difference, others say everything spinning at 10-16000 rpm should be balanced as best as possible.

I bought a Tru Turn spinner because they either come cut for a large prop, or they will custom cut for you for a minimal charge, and they will send it to you balanced. I don't have the means to balance spinners otherwise I would balance all of mine.