The cathedral is free! You only need to buy tickets for the Dome. There are 436!!!! steps to the top. There are other places in Florence that can give you the same views. Toward the top of the Dome, the steps are VERY Narrow. Then you have to walk down all of the them. Hope you have good quads. The statue of David is amazing and was one of my favorite things while in Florence. I used tiqets for all our sites and timed entries. The ticket for the Ufuzzi also included the Prizzi Palace, the Boboli Gardens, and Galileo museum.

Yes, should be fine.

You can see the dome and frescos from the floor of the Duomo. You don't have to climb the dome.

I visited the beginning of may and im sure there were people in shorts. All I can suggest is maybe take a thin sarong with you just in case. Sorry I couldn’t give you a more definitive answer but I hope it helps

I’ll answer this myself now I’ve done it! Yes, you can return down at any point but the climb wasn’t too hard and the current one way system means it wasn’t as claustrophobic at the top as I was worried it might be.

Manica corta e pantaloncini al ginocchio non dovrebbero esserci problemi. Canotta e braghette cortissime da ginnastica anche no.

Cattedrale è cripta, cupola, battistero, museo. Io sono stata fortunata non ho fatto code lunghe quindi non saprei aggiungere altro.

Yes

No. In some areas you may stand off to the side and let others pass but the corridors are narrow and there’s two way traffic going up.