Hello & Welcome

Enjoy your stay! sounds like youve been well advised so far
Yes, joining ABS will save a fortune

Low MPG, ahh well, you can't really pick a car like this on its economy! The cheapness of the car helps though
Insurance, I've renewed this week, and gone with Bell, £260 fully comp, full no claims, no points, ring em, they do play on price

Regular oil changes are the main key! every 5000 recommended
Also clean the breather system, may save you a lot of grief, see the maint guide section.
Make sure the Cambelt & tensioners are changed at at least recommended intervals (4 Y, or 40K)
A coolant flush, with the newer Vauxhall Pink antifreeze wont hurt, and may just help prevent some coolant issues.
Basically give it a good service, and take it from there
Oil, filter, fuel filter, antifreeze, breathers, air filter, check the scuttle drains dont fill with water, they have a habit of getting blocked.
As you are in Derby, may I suggest a trip to Nottingham to see Mark's DTM Calib, he will give the car a tech-2'ing, update any systems that need doing, esp the gearbox which will make the car drive even better, all for a very low price (see the boy's signature for details)