The values for rxvag1, rxvga2, txvga1 and txvga2 are set by YateBTS from the configuration file. The default values in that file should work without changes.
If you are using a Lab Kit, then we calibrated the frequency for you already. If not, for most BladeRF radios we have seen, the frequency offset setting in YateBTS is in the range 165-170.
There are also calibrations for DC offset, but single-carrier GSM is not very sensitive to DC offset.