Congrats! Solid numbers. You should start a fuel log by clicking "garage" way up at the top and putting in your car and your last couple tanks.
Yep, it's OBDII plug and play just like the SGII. Also looks a little sexier, and is much cheaper.
http://www.ultra-gauge.com/
Yes, that's probably lean burn. Once your engine is warmed up just cruise at 60 in 5th and avoid giving it too much throttle (let yourself slow down a bit going up hills). Should keep you in lean burn most of the time. If you hold the throttle steady and listen carefully you should be able to hear the engine die down a little when it goes into lean burn and surge a little when it comes out (usually between 54 and 56 mph for mine).