Hi mate
Ive just rebuilt a 2000 TD5 Defender with my daughter. Most of the advisories are pretty simple to do. If I could offer some advice when you come to buy your Defender I would say that you will need to accept that you will need to get your hands dirty at some point! However they aren't the same as cars and usually have much better access to get the spanners on and spares and parts are really easy to get, and normally pretty reasonably priced. I found over the last 8 months or so that the things I never thought I could ever do, became interesting challenges rather than huge problems. You will also be amazed at the amount of help people will give both ones that you know and others that you don't (eg this forum) - although the immobiliser nearly beat me! For that I called a really nice bloke in Brighton who repairs the 10AS unit, he told me what to do and it fixed the issue. Old school telephone call. What I have found is that people will "pass on" the interest and genuine helpfullness.
So, last bit of advice, get a good socket set, ratchet spanners, angle grinder and 1mm cutting disks, mig welder and a hammer!