Is it necessary [to avoid lines] and is it possible to reserve tickets for the National Museum.
Are tickets required for St. Peters Basilica? Would this be a good thing to do on the day one arrives.
Many thanks for your feedback and vice.
No lines at the National Museum, maybe just a handful of people. St Peter's Basilica is free, no tickets required. You cannot reserve for the Basilica but there is a security check which creates a line. Reserve for the Vatican Museum.
I was surprised by the line for St. Peters Basilica. Guide books are full of info about visiting the vatican museums but I completely failed to anticipate a significant line for St Peters. We arrived, saw a line at least a 1/2 mile long (under sunshine and 32C) and had to say "Okay, we're not going to see St. Peters". There was no line whatsoever for the National Museum.
The line for the basilica is usually long in the mornings as is the line for the vatican museums. If you are seeing the museums you can easily enter the basilica without having to go through security again.
Since you are talking about the day you arrive I will assume that you're talking about seeing the basilica some time after 11. There should be very little line to get into the basilica at that time. Most people try to go first thing in the morning and the others are going through the museums so the security line for the basilica isn't as long in the early afternoon.
Remember to dress properly or you will be denied entrance.
The National Museum is in 3 (4?) separate sites. I only managed to get to 2 of them, Massimo and Altemps - and loved both of them. I cant remember if the ticket was good for more than one day. I went on my last day in Rome.