I use my pointer finger for the brake.
I am always concerned about whether I am pulling the clutch in far enough when I just use my finger.
I find myself using all four fingers sometimes and I hate it when I do it.
How much is enough to shift free and clear without doing any damage?
I use Left Index and Middle for clutch and rest for grip, and for brakes Right Ring and Pinky.
But I avoid using front brakes, coz I been to death and back, and that for more than once on my Enfield.
So my advice is to use rear brakes, but if you are stuck biking in traffic front brakes are only alternative.