A good start would be to check the website and go from there. I don’t know of a good, singular guide unfortunately—there are a couple different ways of going about torrenting on I2P.
I can confirm that torrenting on I2P works quite well! You may have to set aside a couple weeks per movie, though. Still, the torrent selection is decent, if not quite as good as what you would get on the clearnet. You’ll want to check the postman tracker (tracker2.postman.i2p) once you have everything set up.
I don’t use the main YouTube website at all anymore. A big reason for this is that I spend a lot of time using a really weak laptop that tends to struggle with the JavaScript-laden abomination that is modern corporate web design. Firefox itself struggles as well, so I primarily use Luakit with Invidious, which runs peachy. I also put together a local html page for my bookmarks that is generated from Yaml using a small C application (which is not optimal, I know, but I’ve been learning C and this was a good opportunity). Whenever something doesn’t work in Luakit, I evade to Palemoon. I also tried watching YouTube via mpv earlier, and it’s great! It runs infinitely better than any web player at max resolution and buffers the whole video. Never going back.
Those fucks would unplug the entire damn internet in their crusade if they had the ability to