So I think I figured out the problem with my earlier post in case anyone is seeing a similar issue.... Regarding the error:
"You can't leave the EmailAddresses parameter value empty. Property Name: EmailAddresses".
Looking closer at the ExchangeSetupLogs, I was able to find the mailbox this error message was referencing:
FederatedEmail.4c1f4d8b-8179-4148-93bf-00a95fa1e042
A closer look/read says this is the "Discovery Mailbox" which was supposed to be rebuilt from a setup.com prepareschema, setup.com perparead, and setup.com preparedomain.
I found this account in a disabled state (this may be by design), as well as with no email addresses populated in the ProxyAddresses attribute as per ADSIEdit (not sure if it is even supposed to have an email address).
Fix: I re-enabled the account, and entered in an email address for the ProxyAddresses attribute for the discovery mailbox, reran the install, and it processed successfully through past the readiness check and install.
I wonder if this has anything to do with the warning "RUS not available" that we continually see when running the readiness checks - could it be that maybe it wasn't stamped....?
Just wanted to throw that out there in case anyone runs into this, or if anyone can advise me otherwise on the fix I applied (whether or not I should have added the proxy address or enabled the account etc......)
Thanks,
SB