airbox question and gearing concerns

Do i need this silly metal mesh thats behind my air filter? If i remove the mesh filter will the flemsy foam filter be sucked back into the intake? Also-as far as i know, my 00 xrr has stock gearing. I do 99% trail riding (knobbies all year) and i've heard the brp can overheat if you keep it in 1st gear all the time on trails. Should i switch to a 13 tooth front and leave the rear stock? I just got the bike and it has a white bros r4 exhaust, oversized brakes, & renthal bars. Unfortunately i have no idea if the bike has a 170/175 jet kit or if the carb block thingy has been removed. I guess i'm going to have to pull it all apart to see . It seems to run well right now with the exhaust so i kind of want to assume it's been re-jetted.

Link - Read this to get started with some answers.
Link - Sprocket talk.

YES you need to keep that 'silly mesh filter' behind your foam-filter!
It supports the filter, prevents it from being sucked into the engine, but also it prevents the filter from burning when it backfires - mind, some have reported this happening after a spill.
If you do not like the 'dense-ness' of this screen (light hardly is visible through it, it must have quite some resistance) then buy XRsOnly screen, which is a lot more open... and, obviously, will have less protection in the anti-fire department