I took some time to read the post and I will share my thoughts :
Adding and administering domains through Plesk is really easy, I agree, but as you said, you've reached the limit, probably 30. You may always buy an 100 domains license/key, or even unlimited. Your ISP should be able to offer you this, certainly, if you have available funds for this project.
In regards to the other steps : well, it's not easy at all. They will require many hours reading the man pages and running installers your self. Some of them can be done quickly, while other would ask you for more time.
I would recommend you reading the manuals in Google for each question : this will give you more clarity on the processes plus you will be able to do this yourself next time. Example :
Google create new user account
However, there will be some inaccuracy in logs, files, etc, because Plesk uses totally different approach when managing domains and users, so don't be surprised, you will have two logics to follow.