Well... in this point you need to add the harmonic/ behavior of the hardware usual in a real situation in this part of the signal path across the analogue gear with Nebula instance, it´d be basically...
-Buss master of the mixing console -> one Nebula instance with the preset of the emulation of the master buss of the mixing console
-Tape recorder -> one or more Nebula instance with the preset of the tape recorder, tape saturation, tape emulator, ... and a final insert with a plug of a emulation of the tape compression like VTM-M2 or a compressor set to get this type of compression.
Exist the possibility of add some outboard gear (equalizers, compressors, enhancers, ...) between the buss master and the tape recorder, it´s due to differents reasons. In this case the chain must be:
-Buss master of the mixing console
-Outboard gear: equalizers, compressors, enhancers, ... -> One or more Nebula instance with the presets of the hardware that you going to use
The master buss preset use to be included in the mixing consoles Nebula libraries, but it is not always, and when this occur you´ll need to take a buss master preset apart.
In the part of the tape recorder emulation you can use a preset of a tape emulator or a tape recorder, with saturation or not. If you have added saturation in the mix previously, it not use to correct add saturation in the mixdown.
In relation of the outboard gear used in the mixdown, it´s very usual use equalizers/ compressors more typical for mastering purpose, like Pultec EQP1, GML 8200, N**e 2254, etc... It´s very usual in the case of the equalizers just pass the audio signal across it with all parameters set flat for get only the "color" of the equalizer for get a general background in the mix. The compressors are used to glue the mix, get a little more of RMS level and retain peaks.