1) Don't understand your question. What do you mean by "Can we exit leave A/THR at Vfloor"?
(Also it is A.floor, not V.floor - is an angle of attack, not a speed. It is possible to get A.floor protection activate at a speed well above Vls, by pulling back hard enough to increase angle of attack to above the A.floor value)
2) Yes. FAC knows current angle of attack from the probes. FAC also calculates the value of A.floor from the config of the aircraft. FAC makes a simple comparison of the two, and any time AoA > A.floor, activates the protection by signalling the Autothrust to give TOGA.
3) It is confusing and I am not entirely sure. My best guess is option (1). What remains unknown to me is whether the FAC tells the ELAC the value of V.a.prot or whether the ELAC calculates it itself.