Welcome to the forum, airbox melting happens with a few different slip-ons (as well as turn signal melting, but that's a different issue) A good thing to do is to get some washers and longer mount bolts to space the whole thing out away from the box some, even a 1/4" will give some breathing room there, you will have to space both bolts. My FMF Q4 actually came with the spacer needed but it was bike specific.

As for jetting, without a dyno, it's a lot of feel and experimentation. If you go to the KLX thread, read the "Mod day" thread that is sticky'd to the top of the forum, you'll get enough improvement ideas to keep you going for a long time, but as a newbi rider, you can have tons of fun stock. Take your time getting comfy and relaxed on the machine... which as a bonus you can ride off road where there are fewer 4000lb metal meteors to negotiate!