Is it best to book with the museum?
When you book a time is that to see David or enter the building? Is it an all in one ticket?
How far in advance to book? ( April)
You reserve a time to enter the museum. You can see David any time once you are inside the museum.
We were there last May. I booked our reservation a month or two in advance.
Is it best to book with the museum?
Yes.
Always book on the official sites.
https://www.b-ticket.com/b-ticket/firenzemusei/default_eng.aspx.html
Book as soon as tickets are available and as soon as you can commit to an entry date and time.