I have found the English Article of Nintendo about what's the best type of disk: https://www.nintendo.co.uk/Support/Wii-U/Storage/Which-kind-of-USB-HDD-is-suitable-for-use-with-Wii-U-/Which-kind-of-USB-HDD-is-suitable-for-use-with-Wii-U-678127.html
They say it's recomended to have an external power support (like 2 diferent cables, one for data, one for power), it should be something like this (just for reference): https://www.amazon.co.uk/MiniPro-External-Portable-Drive-Nintendo/dp/B00BI9X6WG/ref=mp_s_a_1_12?crid=KSRVMZHTL8JK&keywords=wii+u+usb+storage&qid=1656596587
The Wii U is great. Can you get it cheap anymore though? They've ceased production, so the price is only going to go up, right?
At first I was going to say, yeah, totally, get a Wii U! But then I remembered the console is only part of the investment.
Downloading Games: If you're like me and hate discs, you'll want to get a hard drive like this one. The Wii U only has 32GB of internal storage and some games take a lot of space. For example, Smash Bros is 15.6GB. And yes, you need a weird external USB hard drive with its own wall plug since the console won't provide enough power on its own.
Multi-Player: If you want to play with other people, you'll need some more controllers. Got any WiiMotes laying around? Those work, though many games like Nintendo Land require the Wii Motion Plus ones specifically.
Playing Smash Properly: If you really want the authentic Smash Bros experience, you'll also need a GameCube adaptor or two and a bunch of GameCube controllers. You can use up to 8 controllers in this way.
The costs start to add up a bit. Though, maybe just for me because I like Smash Bros. There's a lot of other good games on there though. Definitely check out Mario 3D World.