Thank you for your detail explanation.
Just to verify my understanding:
1) For the carrier frequency, I think basically you are saying it is in the frequency band stated, but it does mean I can use any frequency for the carrier, there are only some 'allowable' frequency can be used as carrier frequency, and this is depend on the device characteristic.
2) the programmable data rate from 1.2 to 500kBaud is referring to the data rate at the antenna, either in receiver mode (receiver baud rate) or transmitter mode (transmit baud rate).
3) the SPI data rate is going to be limited by the slowest clock of either this transceiver or the MCU, and this data rate is fsclk (since SPI clock in a bit of data every clock edge).
4) continues from 3), fsclk is indeed the input data rate of this transceiver, by choosing the modulation method, the corresponding baud rate can be calculated, and this baud is going to be limited by the send data rate 1.2 to 500kBaud.
Please correct me if I am still misunderstanding.