it started life as a cb100.so look at ebc brakes,and check for your self.when changed use mobile 1 full synthetic oil,changing every few trials.helps to stop horrible noise and feel when hot.
yes a bit powerfull.250 should be top of your list.start with a cheap bike see how you get on,2 stroke would be best easyier to ride.its all down to rider.i saw many years ago mick andrews win a trial on a honda 50 1 mark lost.i rode same trial on a 250 and lost over one hundred marks.
i reckon very good idea.many years ago i put disc on my tl125.but if you keep drum brake clean brake out every time you use bike sand paper on shoes as they go hard and glaze up. when tightening front axle keep front brake on this centrals the shoes.