It's impossible to fuck up such a basic mod. To circumvent region encoding you only need to install the Homebrew channel using the new
letterbomb method. Once you've got the Homebrew Channel installed, no further mods are needed. Just throw GekkoOS onto your SD card and you're good to go.
As long as you're not installing CIOS's (Which are required for running backup discs, dvd players or usb loaders but not for non input-output related homebrew) there is no way fuck up.
4.7GB isn't the actual size of the game. 4.7GB is the total capacity of a single layer Wii disc, so an ISO of that size is almost certainly unscrubbed and still includes the filler file. The actual game should use less data then that. Still I wouldn't be surprised if dual voice did push the game into the dual layer territory.