where can I actually buy my tickets to the museum and the chapel on your site?
"your site" - this is a volunteer helpline. You need to get reservations at the official Vatican site. It's one ticket for the museums and Sistine Chapel. there is a lot of information on another thread here https://www.ricksteves.com/graffiti/helpline/index.cfm/rurl/topic/104023/vatican-museums--sistine-chapell.html It will give you all the information you need. Please read it.