Electron flow at the immediate start of this flip-flop circuit?
Forget about electrons, in this case it is much easier to think about electricity (flowing from + to -).

Also forget about what 'happens in exactly which order'. It does not matter.

At start, assume neither transistor is conducting, hence the collectors will be at ~ 7V. This will cause base current to flow, which in turn causes collector current to flow, which in turn cause the collector voltage to drop. This happens simultaneously for both transistors. They both 'try' to cut of the other one's base current. Due to asymmetries in the circuit (the B of the two transistors will not be the same) one will win, which results in the stable situation where one transistor conducts and the other does not. (until the user preses the button that reverses the situation.)