To your questions:
#1 Yes. You can use the HackMii installer with BannerBomb on an SD card. Once HackMii loads, you will be given a menu that will allow you to uninstall Homebrew.
#2 Yes! Sort of. A guide? I don't know, but I know that both WiiFlow and USB Loader GX have the option to "Install" a game to your HDD attached to your wii. Simply insert the retail disc into the Wii, find your respective loaders Install option and let er rip (no pun intended). In a few minutes, you will have your iso on your HDD.
#3 Maybe? I have read that you can and that some people have been doing it. I don't know if Nintendo servers are clever enough to recognize your playing off of a hard drive instead of a retail cd. I haven't tried it so don't quote me on this. I would research this some more.