My attempt to answer some...
I have never seen any 996 or 986 Porsche use Ohlins coilovers... Motons are the external reservoir of choice... The HR springs are not matched to your struts... you will have improved handling because of the lower CG, but I just don't know how much. You can get brand new PSS9's for 1900... why not go for that? The PSS9's are so widely used in the Porsche world... I love mine and except for an upgrade to Moton's I wouldn't go any other way. And with the upgraded springs I am sure they are even better. You will most likely be able to get away with your stock Droplinks for a weekend or two, but after that they will break. I wish I had a picture to show you the difference between the stockers and the Tarret ones... OEM look like a pencil... Tarrets are just huge... There are post after post over on rennlist about failing stock droplinks with aftermarket sways. I think its essential. Also... the GT3 bar offers more adjustability than the HR front... I believe its cheaper as well (call sunset porsche).
Ive never run nasa, but from what I have heard Hoosiers R6's are the only way to play... a good 1-2 seconds a head of the RA-1s. As for your wheels... if you have OEM 17"x8.5's then I am sure they are great... they will actually weigh just as little as the carrera lightweights... no need to go different there. Biggest weight loss past removing carpet, radio, spare tire/tools, seats, and etc is the Covertible top... chunk it... I believe that is something like 150lbs... mechanism and all... you can put it back in, shouldnt be too hard. Also you shouldn't get any HP increase by chunking the exhaust... so you shouldnt get any dyno points from that, just a hefty loss of weight... Hopefully I didin't miss anything.
