1) Unless you have BootMii installed as boot/, it's considered too risky.Originally Posted by LauraF9145
2) I'm assuming you mean ROM's. But I don't have any experience with those emulators since I have no games for either system. I do know that Not64 is generally considered better than Wii64 in terms of performance and it also works with the newer Wii remotes.
3) As long as you're blocking updates, you should be fine. Be sure to remove any administration tools from the SD card, though (WiiMod AnyTitle Deleter, etc.). There is also a list of things not to do to your Wii. Link in my sig.