Yep, RetroArch Wii's Mednafen VB core isn't really so optimized enough, unlike the standalone version of WiiMednafen by @raz0red, which has improved a lot the Virtual Boy emulation, and now can be used as a Wiiflow plugin.
So i prefer using the standalone one.
I certainly can't say. It's something I haven't tried myself.
Maybe someone here could tell you better.
My "guide" is just showing how to get rid of useless stuff and learning to navigate through directories.
A quick Google search for Hexaeco, says that RetroArch Hexaeco is basically a "get rid of useless stuff" on RetroArch.
So, use that version instead as it's basically what I'm showing in this guide.
I'm afraid it should work. Just set the directories for your device.
Make sure to have Homebrew Channel updated to ios58.
Then make sure the Homebrew Channel is loading the USB (press X on GameCube controller and I think 'Minus' on Wiimote)
After that, load Retroarch and follow the guide in post#1 to set your directories to usb:/ instead of sd:/
Hola amigo, asegúrate de poner las routas en Retroarch con tu usb en vez de sd.
También asegúrate de tener el Hombrew Channel actualizado a ios58 para permitir lectura por USB.