Am new to the forum, 2nd post, so please excuse my ignorance. I purchased an 04 with 48000 miles, loving the car so far but I have a few questions:

1. I have a button that is sitting underneath my accelerator (see pic). Is this OEM or stock or was this car at one time nitrous fed?
2. If its stock, what is it there for?
3. I am 5'8" and I feel too big in this car, I have the seat at its lowest setting and all the way back hitting the back-stop, you larger dudes, what have you done to remedy this?
4. The seat backstop cannot be moved or removed can it?
5. What is the "no brainer" mods to make to this car that are under $1000?