22mpg town driving and 28 mpg motorway driving. To get 28 you have to stop yourself enjoying the car. That is for 2.5 Hawkeye wrx.
Oil change every 3 to 6k miles your choice and depends on type of driving. 10k miles is min 2 oil changes. DIY under 100 quid.
Cambelt £400 just for belt change more if you replace water pump (may as well) and all the guide wheels, tensioner etc.
Tyres at least £100 per corner, foolish to skimp on tyres again my opinion.
DIY is best option I have found cause even Subaru dealerships are clueless paid part swappers with no diagnostic skills or basic understanding of how the cooling system works. Unless you lucky and close to a decent garage. Plus it is way cheaper.
For me tax is £535 and insurance £600. My post code kills my premium. I did 1000 miles last year due to lockdown which is >£1 a mile before I add fuel etc.
Every year when tax is due I think about selling it. Then I realise what would I replace it with and then I drive it and forget the tax bill. Repeat every year.
I would base all your fuel cost on around 25 mpg. I doubt a 2.0 will be much different, may actually be worse.
If you treat it properly it will be fine. If you drive it and treat it like a 18 year old and skimp on maintenance cause you cannot afford this month it will bite you in the !Removed!.