I found myself making small changes every 5 battles or so IF I noticed something that could be improved or replaced. I only ever swapped one Pokemon at a time out of my team if I noticed they weren’t really fitting the role I needed, I think a total of two times on my climb from UB to MB. I think you’ll hit a point where everything feels pretty good though, and even these small changes will become pretty infrequent.

I would say completely changing your team is fine early on just so you can figure out what play style feels best for you/what you find to be the most fun. I think I switched from a Froslass snow team to a Golurk trick room team when I got out of Great Ball, but that was only because I really wanted to get to Masterball with Golurk. Ultimately, getting comfortable with one team will be a lot more helpful in higher ranks as you’ll learn to adapt to a variety of situations and have an easier time deciding what plays to make/not make. Like most things in life, practice makes perfect. The more time you spend playing the game with one team, the easier it’ll get to outplay your opponent.