You can unlock any special stage in any level you want after you collect a 50 rings and go in the big ring in the end, but after you get the crystal you cant get another special stage in the same level, there is 7 special stages so you need 7 acts to finish all of them, choose any act you want, the red rings is for a gold trophy !!!
3) collect 50 rings to get the special ring at the end [make sure you have 50 rings at the end] and in the special stage, if your about to fail, restart! then you will restart at the beginning of the special stage so you dont have to go through the level again
4) im not sure, but i think they are only for the gold trophy
main mario kart wii fc: 2535-5540-1536 alt: 2064-3778-7256