Can I change which buttons my cashiers see first?

Yes. Settings, then Arranging the POS. Drag tabs into the order you want, and drag your busiest dishes into the Most sold tab so they land on the first screen. There is also a box that fills Most sold from what actually sold in the last seven days, counting the counter and your ordering page together. It changes the order of things and nothing else. No dish is hidden and no price moves.