Curriculum Planning for Captivate 2019?

I think you might be overthinking it for a portfolio. You can certainly talk to your potential client about your process for curriculum planning but I wouldn't give them anything other than some sample projects for them to look at. If you created those sample projects for a client you should gain their permission before sharing them. If they are generic provide them with a viewable hyperlink for their viewing purposes; do not give them a source file. eLearning courses should be exactly as long as they need to be. For a portfolio, you want to show your proficiency. If I was hiring you I don't want to see an entire course, but I want you to show me why I should hire you for the job. show me something unique, experiential, effective, engaging and nothing more (think movie trailer). In fact, leave me feeling excited about seeing what you can do with my material.

The 10,000 foot view from my seat looks like this... based on what I think you are driving at.

After it has been determined that training is the solution, I will typically pull a team together and analyze the target audience and intended level of complexity of the content required to meet the training need. (Beginner or advanced level material). Then, we discuss and separate what information the learner NEEDS to know  vs  what information would be NICE to know. We talk about the different ways the learner is able to demonstrate proficiency for each thing they need to know. Assessments can then be created. At that point we can craft the content that will guide them to proficiency as it is to be assessed.

I like to use an ABCD format for objectives.

Here is a link for more information on that...

Objectives: the A.B.C.D. Method: Building Learning Objectives

The training should be as long as necessary to bring the learner to proficiency. You might break down your modules to cover one objective at a time to keep things on the short side. I like chunking and keeping things a little more bite size.