You should average about 30mpg, maybe less if in traffic a lot.
If it hasn’t been done already the rear driver’s side wheel bearing will need replacing at some point; I’ve had five Subes and they’ve all needed it, but nowt else!
On the twin tail pipe models check the rear Y piece thoroughly, and the front of the rear silencers. You’re looking at 3-400 EACH for these three items, though cheap copies are available.
Timing belt is 45k , but check the tensioner and (maybe) the idlers have been done. Budget £3-400 for these at a dealer.
Other than that, it’ll be good for a few hundred thousand miles, with no drama.
They are really comfy cars, with the best front seats I’ve ever had. The rear seats fold perfectly flat in 10 seconds. The radio will be shite!
Great cars!