Welcome to the sport! A few more questions. How much Moto have you and your boy done? How many hrs a year do you expect to put on each bike?
How mechanically inclined are you? What type of Sledder are you? Gotta push the pace and lead the pack or happy pushing a mid pack machine to the limit? It is very important to think about these things and be honest with yourself. snowbikes are a lot like modding sleds used to be before turbos. You spend a ton of money on mods and gadgets for horsepower gains.
If heading west a few times a year, flat landing at home and trail riding in summer a yz450fx is your weapon. The fx is a capable machine in the hills, has a little more gearing for flat landing and is a fantastic trail bike for a 450. The power is there but has excellent manners. Electric start with kick backup, large stator, great airbox setup for snowbikes and Yamaha reliable!! This bike won't beat up on some of the others in the hills but definitely hangs right in there.
As for the kit, Misha's suggestion of the camso is a good one based on the price. We have 1 in our group mounted to the bike mentioned above and it has performed quite well. Only downside to that kit that we found was the ski while on the hard pack trails. Our group of riders are very equal in skill set and though the trail up is not our favorite part of the day, we do have a good time racing, bumping and grinding in the corners. Every rider in our group is a fair amount slower on the trail while on that setup. This includes the owner that has a tonne of seat time on it. When I swapped bikes with him I just assumed he didn't like riding fast on the trail but instantly realized that the ski was much harder to trust while going into corners at high speed. He easily gained an extra gear through the corners on my yeti instantly. We tried quite a few setup changes to fix this and it did help some but still lacks in this department compared to the yeti and aero. Once off trail all 3 kits are very comparable for medium duty riding. The camso lacks for handling big drops ect but most will be happy with it's performance off the trail. I ride yeti and love the products performance but simply can't recommend them based on reliability and customer service. All this said, I would recommend the new aero 129 if you are willing to spend a little more on the kit. Works pretty good in all areas and very reliable with spindle fix. If cost is King, camso all the way and you will still be having a good time.
Start with these simple mods for winter and go from there.
Seat concepts seat(must!)
Intake
Thermostat
Revv up engine blanket
Skid plate
Temp meter
Light
Handguards
Pipe shield
Heated bars(luxury)
