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A: 1)Speed.The “RAM” part of the F-RAM name tells us that it is a RAM, not a ROM.  Of course, EEPROM and Flash are not truly ROMs but writing to them can be very slow.  An F-RAM’s write cycles are completed immediately whereas an EEPROM/flash needs 5 to 10 ms.
2)Low Power Writes.  Writes to the F-RAM cell occur at low voltage and very little current is needed to change the data. With EEPROM and Flash, high voltages (10V charge pump) are needed and writes require 5 ms to complete a page buffer write.  The energy needed is much higher than F-RAM writes.  If E=P*t, then 5ms of write time will necessarily require 200x more energy than F-RAM.
3)High Endurance.  Writes are destructive – and floating gate devices eventually wear out; typical endurance is 100,000 to 1 million cycles. F-RAM experiences 1E12 read/write cycles or greater.

A: You must issue a WREN opcode before the WRITE opcode.  The WREN opcode requires the /CS pin to go low, clock-in the opcode (06h), then /CS must return high.  The WRITE opcode then follows.  The /CS pin goes low, clock-in the opcode (02h), clock-in the address (1 or 2 bytes), clock-in the data (1 or many bytes), then /CS must return high.

A: Two-wire (I²C) is the most common and many micros implement a two-wire dedicated port.  SPI operates at much higher clock rates, up to 20MHz.  For simplicity and the use of fewer I/O micro pins, two-wire is generally used.