I would agree with handling being pretty crap with large wheels, i think i've got 14's onmine and the handling is great, feels as if it has more prescence on the road.
Do not buy a chip off ebay, sorry but some of them are scams and can really screw you over and screw your engine up. Get it from a respectiful shop or fitted by a professional.
Induction kit, air filter and exhaust will give you some more power, which should be ok for you for i now i think.