I will be spending a week in Rome (with a day trip to Florence) in mid-October. For anyone who has traveled at that time, how necessary are advance tickets. I'm planning on two tours (one for the Colosseum/Forum/Palatine and one for the Vatican) so those tickets will be taken care of. I also am pretty sure I should get advance tickets for the Academia in Florence but am unsure about other tickets (Dumo, Santa Croce, San Lorenzo). Any thoughts on how busy it might be in mid-October? TIA!
Accademia definitely get advance tickets. I think the Duomo complex can sell out, so it behooves you to book a ticket in advance, no matter what type of ticket you get. You don't need a ticket for Santa Croce, and for San Lorenzo/Medici Chapels, you only need to book in advance for Michaelangelo's hidden room.
In Rome, the Galleria Borghese also requires advance booking.
The Domus Aurea in Rome requires prebooking. San Clemente may as well, but I don't think you have to worry about early sellouts of full days; you'd probably be safe to check the status of tickets about a week ahead of time.
Since you plan a day trip to Florence, you'll have little timing flexibility and should nail down the necessary tickets early.
Thanks for the replies. You've confirmed what I was thinking.