number 1, sounds like your chain has come loose or stretched, they are normally life of the engine or 100k but sometimes they do go (basically the cam belt)

number 2, the rear callipers are prone to seizing up when the car isnt used a lot, it should be fine now your using it, maybe make sure yo use the brakes quite heavily so make sure the rear callipers get some use for a couple of weeks and they will be fine

number 3, the standard ST engine is very restricted and it will die off when you get past those speeds as the top speed is only 128mph so theres not a lot left really, a K&N will sort that out as the airbox is totally stupid as standard

number 4, the pas system is terrible on the ST, boils all the time and it does make a weird noise under full lock as the pump cant handle it, if the fluid isnt bright red it needs changing again, i used 4 liters to get mine red again on my 1st ST as it was so black from being boiled
and the standard ST suspesion is good, but does have a lot of roll as its so high, i would get your alignment done (proper laser alignment not just tracking)

number 5, the bottom bumper clips are so weak they snap off all the time i wouldnt worry about it, both my ST's have lost them and it causes no problems

number 6, have you tried taking the passenger side one out to see what it is, as im sure its the same

sorry to ramble but i hope i have helped