You probably will need a tethered kill-switch. Can get them at most shops. Other than that you should be good to go. Of course, the more stuff you bolt on it, the better it will, in theory, perform. I would run it as is, just to see if you like the MX scene first. If so, take a look at the fast guy's quad and see what he runs.
Got a question, what do you mean "fuel thingy". Your dealer should have told you "it is race ready, all you need to do is add nerfs, remove headlight, add # plates, add cherry bomb and uncork exhaust". It's already wider and lower to ground, so no a-arms needed. What area and class you goin to race in? Kill switch and some aftermarket bars(if your jumpin)
As ghglenn stated fou MUST have a tether switch, ( dont buy a cheap one, they fail ) you will also have to have number plates on the back fenders, one on the front and one off the rear grab bar.....obtional but worth the effort is one on the back of your chest protector. (It usally stays the cleanest and can always be read)
The Suzuki suspention and arm's are could right out of the box, as you progress with the bigger jumps and more aggresive riding you will want to look at shocks. Spend some time and have your shock adjusted for you and your style of riding......
Tires and wheels are the next thing that we change out right away. But that is even a prefference. ITP hole shots for just about everything except deep wet mud then we switch to a totally different setup that inculdes bigger tires and changing the gear ratios....
The wheels that come with the quad are pretty good put we prefer having the extra support on the back wheels of the Douglas beadlock, we use standard Douglas rims on the front, they are just stronger then the factory ones. Lots of discussion has been had over 8" or 9" once again its a prefference....
Remove all the lights for sure, we even remove the Suzuki starter switch and add a simple single button, add Hand guards, you will need them if you like your hands to stay on the grips.
Depending on your size, were both 6' feet so we like to add a Rox adjustable riser and a different set of bars. (Factory set are pretty soft) Of course with that you have extend the throttle cable and brake lines.
The steering stem is soft also, a fix that we use is a thick walled pipe the perfect dia and length pushed into the factory one....works great.
Just dont roll your quad and you wont have to worry about replacing the bars or stem.....
The factory front bumper, well it dosent stop enough so we use a larger one that comes with a screen or numbered front, we also add a small plate were the head light was to stp some of the dirt and mud from getting to the rad.
Skid Plate....you can buy an alluminum one form dealers, we buy UHMW (Plastic that is really tough) a 2' x 10' sheet runs about $100.00 and cut our own. ( Well worth the money while your learning to jump and then needed when you do....LOL
The stock chain is pretty tough, put pick up a DID oring chain and through it in your tool box.
From there as stated in the previous message, the sky's the limit, shocks, steering stabilizer, exhaust sytem, air system, fuel programer, clutch and brake levers, pistons, cams, cltuch work.......