| Airbox mod is standard on 851/888/900ss/ST2/4/4S which all have the same restrictive airbox design, won't give you much at the top end but will fill in the mid range by quite a large amount, 5-6bhp.
I will let the 851/888 experts on here answer all the other questions.
Enjoy the bike, and welcome, now all you have to do is join.......
John
Growing old-disgracefully! | 
Monty
Threaded Mode