I've decided to start a sims/gaming youtube channel and I was wondering if there is a basic etiquette with using mods and cc. Do I contact creators individually to ask if their creations can appear in a video? Or is it just kinda expected it could be used in videos? I detest nearly all EA hairs and mostly use custom made hairs. I also use mods like MCCC and TOOL.

Thanks

Creations being present in screenshots and videos of the game is pretty much a given part of sharing things for download, so you definitely don't need to ask permission on a person-to-person basis.
I'd say the main piece of etiquette is just to provide credit in the video description. You don't have to link back to every single item, but listing the usernames of whose CC you use is polite.
You could also make a 'Resources' page like many simblr have, on a blog or similar page, where you list what defaults and mods you are using + the usernames of the more general CC. As well as specifying whether you are 'WCIF Friendly', which means you are open to being asked where specific CC came from.

If a specific mod is prevalent in the video, then already having a specific link to it is polite- both as credit, and so that unfamiliar viewers know where those options came from.