If you're on a budget, I would suspect, no I would bet, no I'll guarantee that a pipe and carb work will make more power than a 300cc kit. 2 rwhp gain is not even close. I am thinking I have gained at least 10 horse with all my mods. I was gonna dyno it friday night but they wanted $50, no thanks.
The reason to buy the oem needle and other jets is that you can buy them cheaper than buying the whole dynojet kit. It's like $40 shipped from ronayers.com for the main jet, N1TC needle, circlip, and washer. The dyno kit is like $60 or so.
Regarding the Uni-filter- it IS the choice of all the factory MX teams, I doubt you'll see RC lining up at the gate with a stock filter in his airbox. You decide. For $25 or so, it's a no brainer for me. I wish you could ride my bike just so you can trust me.
Invest your money in a full system, carb mods which is cheap, filter, 13-tooth cs sprocket and you'll be happy. Adjust your suspension settings all to their max and you'll be good to go. Next year do the 300 kit or suspension springs. Changing springs in your forks really isn't that hard anyways. The rear should be ok if you jack the preload up and turn the compression to it's max setting. Unless you're full on MX'ing the thing, you'll be okay. We're not experts on here, and if your a little heavy you'll be okay 95% of the time. Just turn your settings to the max. People who revalve their shocks are usually not as good as they think they are. Some are, but others just like to bring a sticker to the gate.

 

looks good, just don't order that dumb dynojet kit. that will add unnecessary expense. order a 128 main and a 40 pilot (along with the N1TC needle and circlip and washer) if you so choose and it will only be around $10 for both jets- but the 40 pilot is really not necesary. I'd recommend the biggun full evoX system instead of Muzzy. There have been Muzzy owners on here talking about how they had to dent in their pipes to clear the rear footpeg as it is bent as such that it will not clear the footpeg when folded down. Also, there have been some Muzzy pipes sent out with missing spring holders. the biggun uses a clamp and no springs so it's much easier to work with and much much tighter. also, the biggun header is ceramic coated and will not turn colors on you or let stuff burn on. it's just a better overall system imo, but you get what you want. those rubber plugs are exactly what you need to cap off the open parts when you remove the smog system. there are 3 points where you'll use them. also, that sprocket and air filter can be had from denniskirk.com real cheap. just look up a sprocket for an XR650L as it uses the same sprocket, or a Ninja 250. the afam sprocket will probably cost you lots more than a JT like kirk has.