Whatever the stock gap is. IIRC it's .052 Should be on one of the stickers under the hood or on the rad. support.
I would just stick w/ the normal airbox for now and a good paper filter. No need for K&N as the oil just screws up the MAF.
The front sway can be replaced by you no problem. Go with the Dorman bar. Go to RockAuto.com and order it from there. Comes with all new hardware including endlinks. I just put one on my GT and it made a ton of difference over the busted hollow bar the GM put on there. The Dorman bar is solid and HEAVY.
You'll want to flip the bar over so it points away from the exhaust. My Dorman actually had a sticker on it in the center that told me which way to install it, which happened to be the "flipped" version.
I didn't lower my engine cradle to get mine out or back in, but I did pop the drivers' side outer tie rod from the knuckle so I could gain some space.
Doing it by myself it took about 1.5 hours, and most of this was spent getting the new one in place correctly. Just take your time and be sure you don't damage anything else back there while pushing it through as there are steering lines, sensors, etc.. that can get in the way. May be easier to have a buddy help. And this may sound like a PSA, but please be sure to put jackstands under both sides along w/ the jack. You don't want to rock the car off the jack pulling the old one out. Can't imagine a rotor landing on your leg with the weight of the car
Here's a link to the exact bar you want from rockauto-
More Information for DORMAN 927100 Looking at about $79 + shipping