According to an image the typical floor plan for christian basilica is similar to

The typical floor plan for Christian basilica in its earliest form of architecture is similar to the roman pantheons and temples which serve the pagan Gods before Christianity was created. The way the basilica in the Christianity's earliest stage was created to have a meaning in the Christian world and signifies the development of the settlement into a city in a presence of such structures. 

The floor plan of a Christian Basilica is very similar to the Neopythagorean basilica. One example of this is The Porta Maggiore Basilica in Rome, discovered in 1917. It is an underground basilica dated to the first century BC. They have similarities in terms of floor plan and ceiling.

Because most artists loved the way that their men or women that they were to paint/sculpture just the way that they had when they sat and posed and they thought that it looked more i guess

Over head or front lighting is used for a self portrait