Hello :-)
Welcome to the club,
Tyres seem to be a bit of a trade off between mpg/noise don't know weather thats due to being a reinforced tyre or not but i've not managed to find one that does both according to the ratings.
To be fair i have two different brands on each axle both 'intermediate' price range which were on the car when i bought her, the noise isn't an issue as i find the sound proofing in the forester cabin to be excelent, so when i go for new sets it will be more towards the mpg side of things, tyre wear is good too.
Oil i'd use the best you can find, try opie oils (trader on here) good advice and competitive price always has discounts etc.
Mine runs on 10-40 semi synth, being slightly newer yours may be different i'd check the manual,
As for adding a turbo you'd be better off buying a turbod car. As the amount of work involved is alot. just about everything on the engine needs to be replaced or added to.
I'm sure youll be more than happy with your foz and if you do decide to start 'adding' bits 90% of the impreza bits of the same year fit.