Self service for a 300 Disco

Hello there,
We're off on our hols at the weekend to France, just the family and the Disco. It was around a year ago it was last serviced and before we drive off on Sat I'd like to do what I can to minimixe the risks. What I reckon...:

1) change the oil and oil filter
Question - the best oil suitable which is available from Halfords? (my Disco is a S reg diesel, 84000 miles)

2) change the fan belt
Question - is it an easy job to replace?

3) change the air filter

4) check the air in the tyres

5) check liquid levels.

anything else which is quick and easy to do!

Cheers
Alex

change the fuel filter too also, don't forget your headlight aim adjusters.as for your oil i use 15/40 or muti grade, either is fine at this time of year, other than that, have a nice trip