I think Agenda is a great fit for what you describe. There are a number of great topics here in the Talk section of the community that you could use for inspiration. For instance a search on the tag workflow might be a good starting point.
There’s a few different angles to your question, there’s the aspect of how to deal with different strategies and approaches on how to deal with multiple projects and a lot of actionable items, like this one:
Ways how you can use the different features of Agenda in all of this, like:
And some users have gone in a lot of detail on specific organization techniques and how they apply those in Agenda, like
Finally, you might find some inspiration in this article I wrote that is about templates but highlights a few use cases that fit what you’re doing pretty well (client work, creative project ideas, etc):