1- does the gearbox shaft will have problems easily?
it is belt and chain, the final drive is chain. so far there is no problem to the gear
2- is the whole transmission system durable? as in the gears,rollers and beltings etc
manual say change at 20k. but some can go up to 30+k then change
3- how often does tmax need to change battery and recifier?
the depend on how much electric items you add on the bike, mostly same as other type of bikes
4- other then online shopping for aftermarket stuffs anywhere local can get it?
ACM, SBF, motoworld.....etc....