the higher grade fuel is better for the engine and gets you better mileage. even though it's more expensive, it'll work out to the same thing as regular but you're keeping your engine clean. if you still find it's a bit expensive, it's always good to fill up a tank of premium maybe every 4th or 5th tank, though i'd recommend just using premium.
im not sure about the whole leaves thing, but the main thing you need to do with a turbo is make sure you don't start your engine or stop it too quickly. turbos work by having a turbine connected to the engine exhaust that forces air into the intake, compressing more air into a cylinder bla bla blaaa more fuel more power etc. because the turbine is connected to the engine exhaust and spins retardedly fast, it gets really hot, and people can destroy their cars by a) driving it too aggressively right when it's turned on - especially in colder weather - and not warmed up, and b) turning it off after driving it alot, which leaves it sitting around very hot. these problems occur because when you start up and drive hard or stop driving immediately after driving hard the turbo doesn't have oil running through it and with no lubrication and a fast spinning turbine you can fry it. that happened to a friend of mine. cold canada with high revving is a lot of wear and tear. oh, and of course do not ever run your engine out of oil.