I think the first thing that stood out about tmux to me as a beginner was the unnatural use of prefix. I haven't used something like that before where you had to use prefix and then a particular command. It makes sense why it is the way it is, but feels odd in the beginning.

The bottom elements were part of it. Not the host name and time, but the window information. Also, it took a while to remember the default keys to use to get to session management window where tmux displays everything, among other things.

Vim's hjkl make sense as you start using the tool. tmux's Ctrl-B for a prefix doesn't make sense, so that leads to remapping.

I have checked out the UI's you have made - they look great - similar to what I would expect a custom tmux configuration to look like :)