OP - I wouldn't worry too much, I don't get all these 'You're going to need to do X, have to replace Y and going to change Z'
People over worry on the clutch, there is now law to say a clutch breaks at X mileage. It's all down to driver.
If you're patient, you will find a decent zed for 5K. - As for fuel, if a zed is still survivng at 100k mileage (Which will be what you are looking at, at that budget) then it's more than likely going to be fine and ran on 98+.
http://www.350z-uk.com/topic/93486-sold-azure-54-plate-350z-zed-shed-ownedmaintained-for-sale/
Prime example of a perfectly good zed, selling for 5K. You just have to be quick. As I say be patient, as of right now a lot of people seem to be over pricing their zeds a fair bit