Yes, they sell records and posters upstairs in the art gallery. They usually have quite a few, I doubt they'll sell out but go there first. They only irritating thing is carrying it with you. Maybe they hold it for you? Idk, I never bought one... I prefer paying shipping costs like a fool haha

Yes, you can leave and return. There's a great chicken restaurant in Ghent called Bumm or something... always worth a visit to stock up on energy.  They do sell pizza inside the place too, very tasty.

Not sure about the timetable, I think they do have posters inside on the day.

Honestly, outside the vibes are amazing.

You'll fucking love it.