There is already a lot of great advice that has been posted, and I can't add much. But....

Keith Martin is now producing 40 page "dossiers" on collector cars in downloadable format from the roadandtrack.com website. Current market values and tables of recent sales, etc. $12.95 each.

Might be worth it. I have no affiliation with R&T or Keith Martin.

I had an '81 SC Targa, which I sold to buy the Boxster, mainly because I wanted a more modern car.
Ditto to what other have said, tight cockpit, poor to non-existant AC, hard-shifting and somewhat fragile trans. Air box pop-off, Carrera tensioners are must-have upgrades. Most oil leaks are from the oil return tubes (easy to fix), and the oil thermostat (requires dropping engine). If it's leaking from the top of the engine, it is most likely the thermo. housing. A cheap gasket, but getting to it costs $$$.
The SC engine has an extremely rugged bottom end, having inherited the same main and rod bearings from the 3.3 liter Turbo engine, with only 2/3 the hp. Valve guides go bad, which is where a lot of the start-up smoke comes from.
Build quality was outstanding on these cars.
I managed to sell mine at the bottom of the SC market. They have been going up ever since.
http://i169.photobucket.com/albums/u...s/911frt-1.jpg