back up files and mod other console i dunno but i recommend getting moonlight for wii u and vanilla for modded switch. also for wii u get hid to vpad and koopair

another thing get third party stuff like a knock off wii u gamepad charger, wii u power cable, wii u controllers thats about it make sure you have a usb drive for dumping your personal disc copy of games

Buy a white 8gb Wii U, they're guaranteed to not have the nand chip that most commonly fails. (It'd most likely be fine anyways but I opted for that extra safety net.)