Yeah, what Dualstroke said, I couldn't say it any better.
I have a stock KTM 250 in a Blaster and it will outrun a Banshee as is.
100 lbs less weight and 15 more HP.
For swingarm length consider +3" to +4" unless you are dragging or hill climbing.
Any more and all it does is spin.
With +3" I get great traction and can loft at any time with body positioning for control.
My experience with nitrous in Ford Mustangs resulted in head gasket failures and case hardening stripped off the transmission teeth. If you wanna play, ya gotta pay. You better have some spare YZ490 motors available.
Jetting is EVERYTHING with a 2 stroke.
Jetted right it is a powerhouse that will last for years, jetted wrong it is a dog soon to die.