I will recommend pre buying Skip the line tickets so you don't spend a huge amount of time in the queue. What I did was to buy the audio guide. All you need is to either pre buy it or buy the access on the spot. You will need to download the app, put your access code, download the audio guide and bring your own headphones. If you don't bring headphones, that's fine too, you can get a pair for 1 euro from the Basilica.
Indescribably beautiful and absolutely a must see. I went in the middle of summer and it was extremely hot so the largest downside in my experience was the modest clothing requirement. Unfortunately it was just too hot to hike to the top of the dome.