Yes.Q1: Does ‘all of Piccadilly Circus’ mean ‘everywhere in Piccadilly Circus’? So, does ‘clogged up all of Piccadilly Circus’ mean ‘there were too many people in everywhere in Piccadilly Circus and they couldn’t move’?
Meet (so as to reach an agreement). They were either too busy to meet or they used that excuse so that they didn't have to meet.Q2: Does ‘get together’ mean ‘meet’ or ‘reach agreement’ in this case?
Yes.THE TIMES THEY WERE A CHANGIN'
Q3: Does it mean ‘something/someone that is in the process of changing’?