I have found 125's are pretty revy so you will be giving the gearbox a thorough flogging regularly.
As for jumping, 4 strokes arent any different to 2 strokes really,although they are a little heavier.Look at alot of the FMX boys,they are all starting to convert over to 4 strokes for the sheer torque they provide.
Same for monos 4 strokes arent any better or worse thats crap,they will all loft the front wheel easily.
Im 5 foot 11 and ride a KTM 525 and have done for a few years now,and i cant reach the ground flat footed with both feet.But you dont need to, as long as you can reach tippy toe thats enough,you never have/need both feet on the ground anyway as when stationery you should always have 1 foot covering the rear brake pedal.