The MSF recommends 4-finger braking. That said, IMO, with the brakes that most newer bikes have, braking can be accomplished with less than 4 fingers leaving the rest of the little digits for nice smooth throttle control. The goal is to be smooth. Smoothness lends itself to traction management which is the ultimate result. If I need to brake lightly, I'll use 1 finger, 2 for medium braking and 3 for hard braking. One of the problems I often see in new riders is over-braking and some of this can be attributed to using 4 fingers. As an MSF instructor, I will mention that 4 fingers is the preferred method because it provides the most feedback. That's our company line. But, most folks will figure it out and do what feels best for them - that's most important, do what feels best for you.
One of the other related issues I see with new riders is not completely closing the throttle when stopping quickly. This is usually attributed to having the wrist in too high of a position to start with. Wrist should be below the knuckles so that when you reach for the brake lever, you roll the throttle closed. This may help as well.
Lastly, and this is a personal thing, I see many riders with their brake levers too high. The first thing you should do with your new motorcycle is to adjust the controls so that you can reach them and operate them easily and comfortably. With the lever too high, not only is it difficult to get your hand up over the lever, it will add fatigue to your wrist. I adjust my brake lever so that my wrist is straight when braking. Same with the clutch.
Hope some of this helps. It's great to see new riders come along and it's great to listen to questions and experiences. It helps us all and makes us think about what we are doing and how it effects the operation of the bike.
Oh, and yep, they do make mittens for motorcyclists. A lot of the winter gloves are mittens. My rain gloves are mittens.