1: Depends on frame size - you might need an extended crank on the left side to clear motor and exhaust. Won't know until you mock it up though. If you go with a pull start kit, you'll need to extend your right cranks considerably.
2: My fav kit is Raw (@ Products
)- but that's just personal opinon. They're all relatively the same thing, dodge the red filter housing carbs (CNSv2) though. Biggest thing is find a reputable retailer that will stand behind their product with good customer service and a rocking warranty. If you see "Limited Warranty", run like ****, cause if you put gas in it it's void.
3: You can run any kind of brakes, but I suggest a dual pull brake lever so you can get 60-70% rear and and 30-40% front. Side pull caliper is bottom of the barrel, v-brakes are next best, disc is awesome (see #4 for exception), and hub brakes are best. AVOID coaster, they will die so quick and it's dangerous.
4: For wheels and tires you have a few options. For tires, go either heavy duty thorn resistant tubes with liners; slime; and thick knobby tires, you can get a set of armadillo kevlar compound tires with hd thorn resist tubes with liners and slime, myself personally I use solid tires from AmeriTyre - but it takes an inperson custom fit at a local retailer to ensure they work well. For wheels there's options too - there's HD axle kits with hub brakes (threaded lefthanded freewheeling sprockets and a pullstart), ragjoint sprocket mounted on at least 12G or greater spokes, and disc brake rotor mount sprocket (exception in #3). As far as wheel size - 26" is standard. As with driven sprockets vs drive sprockets and their gear ratios, when you go 29"/700cm wheels you have a tough bottom end, but a great top end (and if you build ragjoint style sprocket mount it's more at risk of damaging rims). The smaller wheels (21"-24") will get you more immediate acceleration, but lower top speed at the same peak RPM.