I run scads of open frame motors with DCC. All of mine to date, including very old MG motors, have isolated brushes. In HO I have seen many where there was a metal tab from the motor frame (which is attached to loco frame) to one of the brushes. this has to be removed on these HO motors.
I don't particularly care for sound. It is usually too loud and gets annoying after about 15 minutes of an operating session. I do have some some sound locos that came that way, and some I put a second sound decoder in. but mostly my stuff does not have sound.
My decoder of choice is not a "G-scale" decoder, it is the NCE D408SR. This decoder has a 4 amp continuous rating and a 10 amp stall rating. It will handle any of the older open frame motors from All nation, USH, Max Grey etc. and works well with the Pittmans in the single motor drive Weaver locos. It has 2 light functions plus 5-6 other functions that are programmable and can be used for lights or whatever. In my experience it provides very good motor control.
I don't rate decoders by scale - ie N-scale, HO scale, O scale etc. I rate them by current rating. I have used many decoders that are considered HO sized in newer O Scale locos that do not have heavy current draw. They work fine.
As for motors, I find the old open frame Max Grey motors to be too slow for the my taste and generally replace them with a higher RPM motor. I generally use the AN, USH, CLW and open frame motors unless they have another problem. I have replaced any series wound motors I came across. I think they could be run on DCC with the same decoder, but you would need a reversing circuit between the decoder and motor and that seems like too much work.
