Average salary is about $170,000, RSU grant is somewhere between $260,000 - $300,000 over 4 years.
Number of datapoints on that is somewhere between 20 and 40.
Do note that if you're on the cusp of a level, Facebook can and will put you in a lower level so that you have a chance to excel and get promoted quickly, instead of struggling with adapting and getting put on a PIP.
I don't have that information, and I perhaps was a little too strong in my phrasing. Nevertheless, if you're not confident that you fall at an E5 level when joining, there's a chance you'll come in at E4, which is not necessarily a bad thing. E5 is a terminal level for engineers, in the sense that you can stay there for the rest of your career at Facebook. If you spend too long at E4 without promoting, you may be fired.
You can estimate level based on description here: https://www.quora.com/What-is-the-expectation-out-of-each-so...