Sorry if you misunderstood, there was nothing contradictory. My initial attempts playing around with ISPConfig yielded the APS installer not retrieving the package list. I ran update, after which APS was able to update and pull the package list properly. My "guess" is during the initial setup I had an issue where name resolution on the server stopped working properly for a time, which may have corrupted something along the way.
I then wiped the server with a fresh OS install and followed that guide from the start, APS works fine from the initial install.
As I said - the particular guide you reference works fine with regards to APS. The issues with dovecot are covered in the user comments on the respective pages.
I apologize if this didn't help. Hopefully you can find an answer.