Not sure if vWii hacking is more effort than it's worth for me when my wiiU arrives..
- can I use the same 128GB SD both for wiiU stuff (installing games to usb hdd) and vWii stuff (wii/ngc games in WiiFlow, roms, etc.)?
Yup, this is what I do with mine. Install WiiU games
from the SD card with all the Wii stuff on (not to it)
- can I leave the Wii U formatted hdd always connected or vWii would prompt me to format?
vWii doesn't prompt to format it but at least one loader I use (Nintendont) will not work if the Wii U HD is connected at the same time as the vWii one.
- I have no intention to use a second usb hdd for vWii
What are you using, SD card?
- I have Smash but wrong region so I guess I should use wuphax?
You mean a different region to your console?
- I'd be mad if I brick/ruin vWii and be prevented from using wiiU eShop VC Wii titles
Just follow the instructions to the letter and don't mess about with any unnecesary WADs. Practice on your real Wii if you feel you need to lol.
- I have a real bc Wii for Wii/gc stuff anyway
Basically, since it's in there, can I use my 128GB SD for something vWii related without getting into too many headaches? Maybe just Nintendont via USB Loader GX or via WiiFlow? (again, no usb hdd dedicated to vWii, so I'd have some limits for wii games)
If you had a 128GB SD in there you could use that for all Wii stuff (Wii games, Nintendont, apps etc, and installing Wii U games) and keep your USB HDD for Wii U. That way no nag screens
only problem is USB loader GX doesnt support Wii games from SD