1. I believe I played one of the NES Open golf games, but I never owned it. My first real exposure to the series was Mario Golf for the N64. There's no telling how many hours I put into it. I later played the GBA and 3DS games.I'm not sure how different the 3DS game is from the GameCube version, but I enjoyed it. I don't know if that would have changed if I had played Toadstool Tour previously.
2. Story mode though speed golf would be a close second.
3. It hasn't been officially announced, but I believe that based on some screenshots/video frames, King Boo is a character. I'd like Rosalina, MagiKoopa and Birdo to be included. Maybe Gooigi. For really unlikely characters, why not Geno and Frogfucius? Characters I'd like to NOT be in the game are any baby version of characters. In games like Mario Kart, they take up way too many slots.