OH BOY I LOVE TALKING ABOUT UI.

A lot of UI work is very iterative. You can have a general idea of how things should look/feel, but you won't really know if it's working until you watch people play the game. There's also a matter of what is best practice and how that changes with time. A lot of modern UI design is focused on quality-of-life, convenience and clarity. It's very minimalist, which pushes out how much room you have for theming. I love themed, chunky UI, but it's always at risk of sacrificing clarity and convenience. Striking the balance is really hard. You also need to add to that things like:
- Are you on console? If yes, there are certification requirements with how you're allowed to display buttons.
- Do you have controller support? Navigation with controller VS mouse & keyboard is very different.
- Do you support other languages? Are your buttons big enough to support German, Arabic, Mandarin/Simplified Chinese?
- Do you have universal design language in your UI? Are your rare items blue and are your epic items purple? Do you reload on Square or Triangle? How much are you fulfilling player expectations?

UI is kind of designed in parallel with the entire game, because as features change, so does the UI. I am generally against UI dictating design, but concede that you might also have situations where your game design changes because there's no clear way to display it in the UI.

So to answer the original question, I know a lot of things that won't work, I know a lot of things that will work, but I would put the UI flow through rigorous testing even if I was confident.