Newbie ? about FFT Bins and Resolution BW

If i understand this correctly, the inverse of the sample time
will give us the frequency resolution, which is the same as the
resolution bandwidth on a spectrum analyzer, right?

So if I'm going into an ADC, and i want the receive KTB to stay
14dB or so above the thermal and quantization noise of the ADC,
then i can sample at 100MHz, and the band width can be at
the Nyquist, or 50MHz.  So then i will have a noise floor of
"X" dBm/50MHz.

      But the problem is this "X" dBm/50MHz will be above
the carrier tone of interest, of say "Y" dBm/Hz.  Which is
a very poor S/N ration.

      So can i just increase the sampled time period, so that
the "X" dBm/50MHz noise floor will be reduced by 10*Log (50MHz- RBW)?

      So that if the sample time period is 1 second, then the
noise floor will be at "X" dBm/Hz?  (Normalized to 1 Hz BW)

      Or about a 10Log (50Mhz) = 77dB improvement?

And again, this points to the FFT bin spacing as analogous to
the RBW (resolution bandwidth) on a spectrum analyzer, right?

Thanks much for any professional advice.....