don't worry too much about mileage, my wrx is 330bhp and has over 100k on the clock, fsh with no expense spared.
try to buy from an enthusiast or someone that has owned the car for at least a year or two. if they have only owned it for 6 months, they might have bought it and not realised the running costs and not be able to afford to run it/maintain it. not remapped with mods, run on 95 ron fuel, missed services, or just bought to thrash