Welcome to the forum you'll find the members on here are a friendly and helpful bunch 🙂
I'd recommend watching YouTube videos and buyers guides.
Service history is key, should be full. Check for evidence of oil changes on gearbox and quattro system. With quattro make sure tyre brands/tread match on the same axle as uneven tyre wear can damage the quattro system.
Make sure all electrical items work as these can be expensive to change.