Hey Ben,
Welcome.
Good to have another potential younger member.
£40k sounds like a good price. If buying from a Porsche Centre they should be able to give you servicing prices, I think everything is fixed price now but be prepared for surprises.
Most things will be covered by the extended warranty in the first year. Post year one it is your call as to renew the warranty, it isn't cheap but a lot on here like the peace of mind it brings.
I'd check coil packs have been replaced as this is a common fault on earlier models.
I'd also check if it has had RMS replaced as again these have been known to go and if not covered by warranty would be very expensive.
General running costs. E.g Fuel & Oil
Fuel - first couple of weeks you will burn cash if you are anything like me as the smile the car generates when you give it some is very addictive! Otherwise they are surprising fuel efficient even in London where i live. Even more so at the mo' as i have just been banned for speeding!
Oil - seems to vary car to car but most people carry a litre of oil with them. How much you use again depends on the car and how it is driven.
If you plan on tracking the car...
Tyres aren't cheap as you'd expect, especially the rears.
Pads, pretty cheap but you'd be best upgrading to something more high performance / track based.
Clutch, comes down to driver ability but since you are buying used you don't know who or how it has been driven previous, but they aren't as expensive as you might think.
Other than that I would say they aren't any different to any other car i have ever owned.
I'd suggest taking as many different cars of a similar spec for a test drive as possible.
You'll soon get a feel of what feels right and spot one that doesn't.
Hope the above helps.
Buy one, you won't regret it!
Jim