Check out the guide from Kafluke
Or am I stuck using the memory card I have?
Personally, what I used to do: run a y-cable'd HDD in the back ports, run a 128gb MSD (adapter) in the front, file transfers (as in, you can move saves and games from one area (MSD) to another (HDD)) and wait.
Honestly, don't use memory cards--they'll get corrupted by big games or games that write a lot. Write and read speeds have a noticeable effect, i.e., Bayo 2 on a card will stutter occasionally, but BotW will eventually become corrupted.
I'd save the memory card for other things like retro stuff, as that isn't as demanding as Wii U stuff.
Data management in the settings.
Heads-up: if you're moving games, always move/copy the game before the save or else you'll have a bad time.
I also think there's a way around the 300 title limit, but I can't remember exactly.
As for Haxchii, keep the hax game on the NAND, with the files on the SD.
have the wiiu format the drive
Yes. It'll be fine if you transfer stuff over and keep the MSD for transfer installs--don't forget about splitting your files if you want bigger games.