Hi Andrew, from Nashville,
I have three front engine wasserpumpers, and they generally seem to be very well protected from rust, having been dipped in preservative (and galvanized) at the factory. Repair areas will be "on their own" due to the workmanship employed at the time. You're lucky, in UK, to have such great specialty shops, so all it takes is a wad of cash. Sorry for sounding heartless!
My 928 has a bubble at the bottom of the rear window. When this car goes in for painting, I'll have to remove the window, and have that section cut and patched appropriately, so as to not put the expensive paint job at risk. No need painting over poor prep work.
Take it easy and slow, do it right. Working on a Porsche body is really not any different than most other cars.
Regards,
P
Nashville