1.- you can add a rack-n-pinion to any buggy/kart (welding required).Your control on the suspension will be tougher to deal with, the traits of the single A-arm is what gives you that washed out feeling.
2. you'll have to measure the tire clearance at the front for rubbing before knowing how big the tire can increase-16"-19" height may be achievable but will probably require an 8" rim- I believe yours are 6" rims.Putting a larger tire/wheel at the front will help with the steering.
3.
https://www.*************.com/item.a...-1721&catname= will probably fit and add some softer/longer travel.