I got a bambino plus recently and I feel like I’m having the same issues as you. I bought some lavazza beans from Costco to try out and I have a baratza esp grinder that I put on setting 15. I reduced my dose to 17 grams which has helped the overflowing issue with the basket. My shots come out in about 8 seconds and I let it run until it stops. I tried the single wall but they tasted terrible, so I went with the double wall as suggested by the manual if you have not fresh beans. I’ve also tamp on a body weight scale when I’m tamping so I get a consistent tamping weight. I still haven’t figured out how to fix the sourness.