Does it cost more on Sunday?

I don't know but dont think so. Make reservations

Technically yes, also it costs a lot more to make reservations online. If I were you I would go @11am on a sunday with your group and you will be racing by 11:30, it is very fun but it’s very expensive once you break down how many laps you get per race and learn that the first two laps are slowed for warm up, honestly it’s only worth the money to go once and then if you like it save up for your own kart you can take to a track.

You don't have to make reservations but it's better if you have more then 4 people with you