As far as the bolts you need to get assorted sizes
4) 4mm for the mag cover
The most popular size is 6mm for Clutch cover, Sprocket cover, Cases
Intake and exhaust 6mm threaded rod and possible head studs depending on engine. I have a completly different engin than most members. I have a Grubee 48cc Spitfire Roundhead, so lengths vary, but having an assortment is always a good thing. You can start with 1/2 doz of each lenghts 25, 35, 50, 75mm should be the longest you would need except for maybe the rear mount. Hope this helps.....
I would also pick up some 6mm washers, lockwasher, and nylock nuts. And some Red Loctite........