I keep telling myself not to start until I finish my casual 100% run, and the thought of having to wave the JoyCons making my arms ache doesn't fill me with a lot of hope. And I always see new WR's being uploaded on the subreddit, it's making me wonder how competitive it actually is.

Plus there would be a LOT of memorising involved, or at least partially recognising how to complete moons from notes. And there's like 800 of them isn't there? What do you guys think?

It depends what category you want to run. For any%, there's only 124 moons you need to worry about. If you want to do All Unique Moons, it's 880 moons.

The game is extremely competitive in any%, but it's not very competitive in the rest of the categories.

For joycons, you can either attach it to the spine (which usually gives people issues with rolling), have it separated, or use a pro controller.

The memorization isn't too bad. You mostly want to memorize what moons you need to get-I recommend to not worry too much how optimal you are trying to reach the moon as a beginner.

There's also a lot of resources and guides for the any% route along with a really big community that'll love to help you out with any category. Good luck.

You could also try out ILs first, completing a whole world with the same moons you would use in a full-game Any%, helps a lot memorizing it too

Compared to some games, Odyssey any% routes are generally very easy. There are many guides out there (check out smallant's guides on YouTube), and there are lots of beginner strategies and such. It doesn't take too long to learn the routes, even without muscle memory you shouldn't have too much of a problem with Odyssey.

Also worth noting, "not being competitive" really means not optimized in this case. I bet if you were to find improvements, you would inspire some rivalry, then suddenly it's competitive.