from memory exhaust is not allowed to be more then 90 DB at a specific rev range, some shops will pass it at 93 max
max wheel size depends on ur rolling diameter as to not put the speedo out..wheel diameter and tyre profile effect this... rule of thumb is u can go 2 inches bigger on the rim then stcok. There are websites that do conversions or go to ur local tyre shop and theyll be able to tell u
100 mm at the lowest point is the lowest u can go, this includes exhaust