[drburton]

Welcome to the forum!

Couple of thoughts off the top of my head:

1) In my opinion a Boxster is not a great car to own if it is your intention to use aftermarket parts to add power. Generally speaking it is extremely expensive with nominal gains.
2) If you get a Boxster I would look to buy a newer one with a larger displacement, if power is a concern.
3) No experience on adding a supercharger, can't really help you there.
4) Boxster vs. 911. You can find lots of threads on this but to sum it up, the Boxster has better balance with the mid-engine the 911 is very *ss heavy. But the 911 has bigger engines with more torque and a backseat. I think the 911 can be a monster on the track with a more experienced driver. A Boxster is more foregiving and much easier to track. The Cayman is probably the best overall from a pure balance perspective.
5) For suspensions, exhaust, header etc.. there are lots of options. Do some thread searching.

Hope this helps.