which upgrades are a must do. i am buygin my son a new 05 trx 90. it is box stock. so what mods should i do first. For now i want to run the motor stock till he gets used to it. then i want to do intake and exhaust. Suspensions is top of the to do list. I plan on using noe of those bolt on dual aarm kits. What about a cdi is it necessary.

Suspension - what shocks?
what arms?
swing arm length/builder?
rear shock?

motor - what pipe?
cdi?
intake?

tires - what wheeels offset/bolt pattern?
which tires/size?

And please post any relavant links so i can finsd an reasearch the info