Which ticket type for Vatican Galleries

They are on sale through May 4th (the 5th is a Sunday and the museums are not open) so roughly 60 days in advance.
If the day/ticket you're looking at shows as "Not bookable" then they're not on sale yet for that day.

Thanks so much!!I was just wanting to know how far out they book. So 60 days. Great!

All tickets to the Vatican Museums include the Sistine Chapel and whatever other parts of the Museums are open that day. You will usually see some areas roped off, but I doubt it varies much from day to day. The standard ticket is listed as "Admission tickets - Vatican Museums and Sistine Chapel". It normally appears first on the list of ticket types. The other tickets add extra features like tours, which you might want, but the standard ticket allows you to explore whatever is open that day.

Note that online tickets for the Vatican Museums sell out ahead of time. As we move into busier periods of the year, the tickets will sell out earlier and earlier. Tickets are timed, and the last few tickets available for a day may be for the last entry period, which isn't desirable if there's a lot you want to see. This means the ticket situation may be worse than it initially seems to be.

You can start your ticket search here: https://tickets.museivaticani.va/home/calendar/visit/Biglietti-Musei

The standard entry ticket sold by the Museum itself, gives you access to just about the entire museum to include the Sistine.

I've always gone with a tour provider, such as Walks of Italy; while you pay more, and waiting in line is nominal, you have a guide who's able to talk and give perspective on what you're looking at. I've done another tour with a different guide service, where the focus was on Ancient Roman & Greek work...which also included the Sistine. Other tours may focus on the architecture, the tapestries, the dome, the crypts, etc.... Much depends on your interests and how much time you'd like to spend.