Does the set only include one kart? Can I still play with only one set? Can I play with multiple sets?

Each set includes the kart and the gates needed for creating the course, as well as optional arrow signboards. The Mario Kart Live: Home Circuit software is download only, so just follow the included instructions to download it from the Nintendo eShop. (The software is free of charge.)

If you buy one set, one player can play. If you have four Nintendo Switch systems and four karts, up to four players can race together.