Pay attention to feelings of overwhelm
The suggestions above are very good in terms of deconstructing some of the thinking process and suggesting different ways you could handle this project.
I simply want to address the feeling of overwhelm. That is something that is very important to pay attention to because if your lists repel you in any way, you will be less likely to stick with your system and move forward on things you'd like to get done.
I encourage you to use the solution that works best for you.
There is often a conflict within practitioners between what I think I "should" do, and what I feel will work best for me based on the suggested best practices.
One option is simply to put only the amount of parallel next actions that doesn't feel overwhelming to you. Just because there are 5 possible next actions doesn't mean you're obligated by "GTD regulation" to put them on your lists. There is nothing wrong with just putting one of the possibilities if that is what feels good to you.
And I agree, some future actions will be apparent once you've completed the next one. Others can be placed in Project Support (notes), and yes, you can opt to break stuff up into more than one project.
The goal is to find the way that matches your way of thinking, and most importantly, that when you look at your lists, you're attracted to the doing and not repelled by it. The latter is the part I wanted to highlight as critical, because it will determine the success of your system. Emotions are usually stronger than logic, and if you're feeling overwhelmed, no matter how correct your system is from a GTD standpoint, chances are you will not use it. A system can only be effective if you use it.
Presenter & Coach
David Allen Company