Hello my b7 1.9 avant has just hit 161k everything is running great as its been looked after very well... but i have recently taken on a job which means I'll be doing 250 miles a week instead of 50. What advice can you give me apart from keeping on top of oil changes.

Also what are some good long life tyres? It currently has Pirelli cinturato p7s on the front and avon zz3 on the rear these was on when i brought it

 

Those Pirelli's are good.Do a little research tho,because not all the Cinturatos are
high mileage.I would put the same tire ALL the way around,Audi recommends it.
Higher mileage oil might save you a few bucks,depending on how often you change your oil(and depending if your car burns it).Make sure you set your car tire pressures to 35psi.
Check every week.That alone should save you plenty in a years time.

 

Keep in mind your timing belt will be coming due as well. Really for a high mileage car as long as you keep it up it should keep running for you. You might start to run into items that need to be replaced soon (battery, serpintine belt, etc...), but once again if the car is in good shape you should be fine. I think age of the car affects future cost more than miles on the car.