I'm using the Redox (almost the Ergodox layout) for about two years now and I'm a big fan of the ortholinear key layout which (at least for me) was as much of an ergonomic factor as the split. So I would not get the UHK (but every hand is different).
The adjustment is not that bad. Just know that you are forced to learn touch typing (opting for blank key caps helped me a lot with that). When you are forced you usually learn this pretty quick. Just getting fast takes more effort.
If you want to learn vim keybindings, I would stay with the usual QWERTY layout as vim keybindings are optimized around the QWERTY homerow. In my opinion, other layouts like Dvorak or Colemac mess up at least a part of what makes vim keybindings great.
Of cause you could remap some keys like HJKL (left down up right) but you would have to do so in every application you would like to use vim keybindings. And what would you do if you are editing a file with vim on a remote server?
IMO alternative layouts are a bit overrated. An ergonomic keyboard takes you most of the way. If you stick with QWERTY you also won't forget how to use your co-workers keyboard.