I believe you can SET bots in multiplayer. . . not sure, though.
F-Zero GX is a great game, Mario Kart promises to be, and I own Kirby Air Ride, and it's also tons of fun (the city mode is extremely addictive!). I've only played it with two players, so four players is probably even better. Depends on whether you want a serious or hard one, or a fun easy one.