omniHUD editing is a lot of trial and error. Most files aren't named too far fetched compared to what they do in game. You also find that a lot of files that have the most issues are ones that are hard to edit because of their unwillingness to change, otherwise, HUD editing is almost too easy.
I've gotten to that point where I almost know every file in a HUD. I've worked on HUDs for an extensive amount of time so it's natural I'd have picked up the ability to remember what I'm editing. By going through every file and changing something, you end up learning what the file controls. Trial and error.
I find a lot of questions I get about HUD editing are about how something won't change in a file despite the values being changed. You gotta remember that you're not completely tied down to what valve gives you in a file. You can add almost anything to a file as long as it's not too specific. The most common is backgrounds. Just because valve have put a background into a file that doesn't edit very well doesn't mean you can't remove that background and add your own. Learn to break things on purpose and fix them in a different way.
In terms of learning things, I did start a YouTube HUD editing tutorial series recently, although I got a bit busy with other stuff, so I put them on hold. I'll try and do some real soon and cover some different topics if you'd like.
Sorry if this post is kind of a mess, wrote it on a small work break.
Please do continue that YouTube series, it is incredibly useful and easy to follow.