HELP regarding B210 and B205mini-i in simulink

I am using B210 and B205mini-i. I have a few doubts. I hope you can help me. Doubts are listed below:

1) In matlab simulink there is an option of master clock rate, but no description can you please elaborate on that. Also it has some limit i.e., 56e6 Hz what happens if I use more than this limit.

2) Is there any relation to select center frequency, master clock rate, interpolation/decimation factor and gain.

3) Can you give the range of suitable gain.

4) There is an example in matlab for frequency calibration while using that when I plot the spectrum it's the same with or without antenna which suggest it is not working correctly. Can you suggest where the problem might be?

5) I am trying to send a simple QPSK signal and receive(example from matlab simulink). All blocks work fine in simulation but when I use USRP for Tx/Rx BER is always 0.5 and I think usrp is not detecting any signal. Is there any parameter mismatch?