How to estimate the noise level of the receiver?

Now I am dealing with a receiver, made up of two stage frequency conversion. The rf input level of the mixers is about -30dBm. With a conversion loss of about 8dB, the output of the second mixer is about -38dBm. The total maximum gain after the second mixer is about 60dB and the noise figure after the second mixer is about 10dB, then what is the noise level of the receiver? Is it about (-174dBm/Hz+60dB+10*log(RBW)+10dB) or (-174dBm-(-38dBm)+60dB+10*log（RBW）+10dB)？In fact, the total noise figure of the system is about 18dB and the maximum system gain is about 30dB. I am afraid that even the total noise figure is 18dB, the receiver output noise level is not (-174dBm/Hz+30dB+10*log(RBW)+18dB). Would someone give me some suggestions? I set most gain in the second IF. In addtion, there are some attenuators and a LNA before the first mixer and the gain between the two mixers is about 0dB.

You have to specify the entire RX chain parameters, as LNA gain, LNA NF, system RBW, etc, to be able to calculate the RX noise floor.

Use the freeware program AppCAD to do the system analysis (Signal-Systems/NoiseCalc):

AppCAD

It looks that your calculation is correct but the real input to your equation may be not correct. The best way is to measure the noise figure.

If you can measure the output noise power before detector (before any non-linear element), then you could introduce two known noise-power levels to receiver input, then use the Y-factor method to obtain the noise figure.
If the receiver operates at a frequency > 1 GHz, a connected antenna can be used as the noise source, by pointing it at a house wall or ground for ~300 K noise-temperature input, and to the sky for ~ 50 K. You can also connect a matched resistor termination to receiver input; at ambient temperature it will again generate 300 K; if you then cool it by dry ice or liquid nitrogen, another input noise temperature can be obtained. You can also immerse the resistor in boiling water to get ~400K.
The easiest way is to measure receiver NF with a NF meter if you have access to it.