Booking venue tickets in Italy

Use the official website for the specific attraction whenever possible. Only use tour company websites if you want a tour. I'm confused why anyone would use an accommodation booking agency for sightseeing tickets.

A couple of the official ticketing sites for 4 top attractions to get you started:

Vatican Museums:
https://www.museivaticani.va/content/museivaticani/en.html

St Peter's:
https://www.basilicasanpietro.va/en/

Colosseum/Palatine/Forum:
https://ticketing.colosseo.it/en/

Galleria Borghese tickets
https://www.tosc.it/en/artist/galleria-borghese/galleria-borghese-2253937/

Give a shout if there are other attractions you wish to see that we could provide ticketing info for (if advance tickets are necessary for them,)

I don't use airbnb accommodations so can't help you there. A suggestion? A good guidebook is going to be very helpful for choosing attractions you wish to see. As well, a search of the RS forums will turn up a wealth of recommendations for everything from walking tours to cooking classes to accommodations. Just be sure to use the more recent threads - from within the last year is probably best. - that those going back too much further than that.

Thank you
Is there any particular tour guide company that is better?
Airbnb just had attraction suggestion and some looked interesting, but I’m not sure who they are booked through.
In the sienna area is there a tour for olives/olive oils? Or is that better in another area?

Tickets in Florence to see David. How far ahead to book. What is the museum site? If you book a specific time is that to enter or see David? How long can you be in the museum?
Thanks

Your question about "David" (he's at the Accademia in Florence) was answered in your other post.
Can't help with oil tours, sorry, but I see that Roberto has provided some good ideas in your other post for that too,