Welcome Jeremy.
1) have a look at Toyo Proxys on Demon Tweeks website, great tyre and excellent value.
Sadly only available in 205/55 x15 so there will be a loss of ground clearance and the speedo will read marginally fast. I would personally recommend the Avon ZV5 (now superseded by the ZV7?) in the 205/60 x 15 size. Good value and reasonable grip , admittedly not quite as good as the Toyo Proxes T1 R
On the exhaust system question it depends what how much you want to spend and if you want a single solution that will last for decades. The latter is the Librands/Harpers/HoE system which all release more power from the engine, as the standard cast iron manifolds and the 90 deg bend that ~MMC use , are notoriously restrictive. Personally I would go with the Librands system as that has excellent credentials , many happy +8 owners , and good results (but do get it fitted professionally , even a good DIY mechanic with facilities will struggle to fit it inside 4 days, although perhaps the newer non-crossover system is easier)
