I'm very interested in using this UI; however, I have the spells on my hotbars set up on each of my alts the way I want them. Would I have to recreate the spell setups on all my hotbars for all my alts when I install this UI?
no, that data is saved at the server and is unaffected by the UI you run(although you can store them locally via /save_hotkeys). You may just need to rearrange your hotbars, but not the actual spells on them.