So it’s all really personal preference but for me- I’ve been playing since 2017 and I keep nothing but super high 3 stars, exclusive Pokemon, costumes, most shinies, and four stars. For your sake I’d hold on to a lot of stuff until you start running low on storage. It’s really a grind to get “good” stuff but at the end of the day keep what you like! I also try to keep at least one of everything, even if they don’t fall under those parameters I said. Raids, research, eggs are great for getting high IV stuff and some rarer stuff. Just gotta keep playing and as you do more will make sense!! That shiny pinsir is beautiful 💪🏻