Unless you're visiting the abbey for individual prayer, you will need to buy a ticket to enter Westminster Abbey. As the abbey is a working church, it may be closed partially or completely for events or ceremonies.
Westminster Abbey and Westminster Cathedral are two separate buildings. Westminster Abbey is an Anglican Church, whereas Westminster Cathedral is a Roman Catholic one. The two buildings are separated by 400m not to mention almost 1,000 years of history, with Westminster Cathedral consecrated in 1910.
Yes, visitors may take personal photographs whilst in Westminster Abbey. Please don't use flash, selfie sticks, or tripods. You cannot take video recordings. During services, you cannot take photos.
Palace of WestminsterBy waving your hand you can find the device you need. Visitor toilets and changing facilities are also on the first floor. These are off Lower Waiting Hall and close to Central Lobby.
There are over 3000 people buried at Westminster Abbey, which includes 30 kings and queens of England and hundreds of influential figures from various disciplines.