@ bigbbrother...............
i think you have made the right decision of buying a mini with square lights. your problems and probable solutions are here under.....
The swaying part is becos your front suspension needs replacement. that would also include your shock absorbers. the rear shocks needs to be inspected.
the hissing sound is from the Turbo if it has one. it should start whisteling from 2000 rpm i think and will continue to increase. if it is a non turbo model it could be a leak in the silencer.
and yes the speed part......if you have proper original plugs installed and clean air filter it should do 130. this is a small car bro you will have to compromise on speed here. with CNG it should do 110-115......
i dont see the problem in your cng installation but i see it in the tune up. there are after market plugs available but dont go for these. Buy original since they will last a year plus.
take care and welcome to the world of 4x4.