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.
Yes, if you know your schedule and don't mind being locked in to that day.
Alternatively you pay (more) for a guided tour that includes a ticket, which can be booked the day before or same day.
All on one ticket. David is one of the pieces on display.