The s23u is really nice, downsides? Probably the weight and not being able to use a screen protector with a case. The only way to know if you made the right choice is by comparing the features and differences between the 2 and seeing whether you would actually use those features. For me I bought the ultra for the bigger screen, storage, and cpu. I never use my pen. Screen resolution between the s23+ and s23u isnt something you’ll notice unless you look closely due to the ppi being high for a small screen. If you end up deciding that the ultra is worth, I would wait a a few months for the s24’s to be announced and check reviews on it.
Case wise, Spigen no doubt. Galaxy buds however in my experience have been great in terms of sound and fit. Both of these however is very subjective lol, some people dont like the harmen target sound curve and also everyone’s ears are different so fitment might vary.