Consider buying the 100 days card; good for 10 tickets with 2 euros reduction per ticket. Can be used to buy tickets online & can be shared with friends.
The ticket automats don't take international cards, and when you buy tickets from the cashier they won't ask you where you want to sit (you can try and ask but still weird).Toilets aren't free too btw
Credit cards are NOT accepted here. Only Bancontact at the kiosks and Bancontact and cash at the register. There's a Fortis cash point across from the main entrance outside though.