So there are a lot of videos and some of them might be worth watching. I doubt anyone watched the whole channel in it's entirety, but still could somebody who did watch some of it say which videos were useful and which are no longer relevant?

It depends what you're looking for.

The tutorials on 4coder.net are probably still relevant.

And there is Customization layer - getting started on the wiki that should still be accurate, but doesn't discuss some of the latest things like using the render caller to highlight things.

Where are the tutorials now that the website has updated? (Link is broken and I don't see a tutorials section on the current site.)

(Edit: well this is somewhat helpful: https://web.archive.org/web/20190.../http://4coder.net/tutorials.html)

I think (I don't actually know) that Allen is preparing the launch of 4coder 4.1.0 and that the tutorials and documentation for previous version will be out of date when 4.1.0 comes out. You may still find some of the videos on Allen's youtube channel.

If you have specific questions meanwhile you can ask them in the forums.