Will not answer all the questions at once, bear with me please. Assuming you have Programming and calibration guide.
(1) - Two options here: (a) you can generate single tone using TxTSG which is quite poor and can generate two frequencies only - clock of TxTSP divided by 4 or by 8 and divided by interpolation factor; (b) you can generate single tone using TxNCO. For option (a) you bypass all the modules in TxTSP except interpolation, set to provide data from TxTSG instead of LML interface (INSEL 0x0200[2] = 1) and control generated frequency by TSGFCW 0x0200[8:7].
(2) You can use the same approac as in (1) just other way round. You just provided RxTSG data instead of ADC. Check RxTSP control diagram in Programming and calibration guide.
(3) Check XBUF control diagram in Programming and calibration guide.