Thank you for the question.
Reverb and submixes can be a tad tedious but I did manage to find some relevant documentation.
For the reverb: you can find those in your Sound Class asset or more indepth with the envelopes in the MasterReverbSubmixDefault asset (found in the engine folder).
If you intend to use any engine assets, please consider duplicating it and manipulating your copied asset to fit your preferences.
Here is some helpful documentation on submixes if this interests you.