All the normal filters changed plus the breather filter by the air filter, plus brake fluid. Oil wasn't in a good way, very dark - last changed 6000 miles ago but nearly 2 years.

Overall they said the car was in good condition, especially underneath which was very clean with no leaks or damage - all good news.

The bad news - two tyres are near the limit, the other two tyres are around 3mm; rear discs are corroded although pads are in good condition but he advises to change them.

So questions are:
1. Should I change the disc now? Or wait till pads are worn? If I do how easy is it to change the rear discs, I found a video link for some US website and they were doing the front, all looks straight forward but I'd need to purchase car stands, jack and torque wrench which whilst they are useful long term I'm not sure if its worth the hassle especially if I come to do it and don't feel confident that I'm not going to mess it up.

2. Tyres - thinking part worn, currently running Pirelli Scorpion Zero's - looking on eBay, you can get ones around the 5-6mm for £80, is it false economy though buying part worn?

Never let the tyres get that low. I think the car is dangerous in wet weather, aquaplaning, unless you have around 4-5mm.
You can buy new Nexens for under £100.
All discs get rusty looking, are they badly lipped? Do they look worn? When was mot last carried out? Previously..
Vogue SE TD6
Defender 90 2.4
Defender 110 TD5
Vogue 3.5 EFI

MOT is due August, disc is corroded on the outer 3 cm, looks like the pads are only using 70% of the disc surface.

Never heard of Nexen, but a search on here shows that a few people use them. Quick google found these

http://www.ears.co.uk/Tyres-Tyres-Mid-Bran..._info.html

Have just bought a RR from a main dealer who supplied it with 4 x brand new Nexen Rodian.

I'd never heard of them either but they [dealer and forum reviews] reckon they are long lasting and a very good all round tyre. They seem fine. Quiet and look good enough on the wheel too.. and by god they are cheap if they are as good as the assessment of the dealer and other reviews.

And... if you buy part worn and a tyre or consequential problem arises/ you won't have a leg to stand on whereas if you buy a new tyre that cost the same price...)