The hard start and non running situation could be more than one thing I would start with the carb clean it thouroughly if that does not work check your timing. The problem withit going into nuetral, my 125m did that for the whole amount of time I owned it and i abused it alot and it never got worse, I would run it till something worse happens, though other members probably wont agree with that. As for the brake, there should be a place for a cable to go so just buy the cable handle and perch and put it on.
1985 ATC125M: Parts
1985 ATC200S: 84 200S Bottem end, 200x Head, 200x Carb, S&S Cycle Exhaust, Wiseco 10.25:1 Piston, Reground Cam with About 1mm more lift(unknown specs).
1988 TRX250X
1983 ATC200E: Total Pile.
"Bout Tree Fiddy" Master of Thy 22RE