Southern Norway Coast during Easter

hei! looking to plan a 4 day trip from Oslo to southern norway (between Kristiansand and Mandal/Lyngdal, possibly Flekkesund) only using train/bus during Easter holidays. However, I'm seeing that a lot of the local buses are not running Thursday - Sunday... I think the Mandal buses will be running (based on Vy), but not in Flekkesund, so we will have to omit that (unless someone can correct me). Does anyone have insight on if all shops/restaurants/groceries will be closed Thursday, Friday, and Saturday, or just Sunday?

We would like a relaxing trip with beaches, hikes, and pretty villages. Thinking of Mandal, Kristiansand (I see the art museum will even be open Easter), and open to any other cute places! Takk in advance!