johnbetando said:

…I’d like to get some planning and organization to my gameplay before building in an engine.

To preface what I've wrote, I just want to give my definition of what it is to think: to speculate on and experiment with the relationships between two or more observed objects, phenomena etc.

Short (slightly vague) answer:

I think Tom's suggestions are great, but my one warning will be don't think too far ahead using one medium, especially if it's not the medium you want to present your ideas through, in this case a game engine in the form of a video game! It might not turn out how you thought about it. Be incremental and exploratory etc. Be a hands-on adventurer with your thinking.

Long answer:

I believe that Humans think through (or on) mediums, such as a game engine, a piece of paper or in our mind's eye. Therefore, I believe building the game is the same thing as planning or organising the game play. Each medium feels different and has different strengths and weaknesses when it comes to thinking about and expressing your ideas. It's for this reason that I don't believe there's such a thing as first “validating” ideas on, say, a piece of paper. I believe what really happens in that situation is: a person does their thinking through the piece of paper and then they attempt to translate that thinking on to a different medium, say a game engine.

I believe the cost and difficulty of translating to a different medium gets high and fast depending on “how much thinking” you did. The “higher” you built up the idea of the object, the more difficult it is to knock down or extend after-the-fact, especially when the feeling, behaviour, tone etc. of the thinking on the object becomes so exponentially different on the new medium. I personally do this all the time: I get too far ahead with dreaming up ideas in my mind's eye and they're suddenly too big or too “complete”, I struggle to find the willpower to try and translate them to, say, writing. It's also stressful when the translation isn't accurate and it can't be accurate because it's a different medium. What might had been “valid” on paper may not be “valid” in the next medium. It's like when someone says “the photo doesn't do it justice” vs. how you feel and what you sense as you stood there taking the photo or sometimes you visit some place based on the photos and explanations but it's underwhelming when you get there. If you introduce a new instrument in to an arrangement it might change the nature of the song entirely, causing you to go back and tweak several elements of the song, which may be costly depending on how built up the song already is etc.

In your situation, playing with some game mechanics in Excel isn't a bad idea at all, but don't wait too long to translate it into a game engine to see how it behaves and influences your thinking there. Let that inform how you approach your thinking in excel in the next push - develop the idea evenly and in tandem on all the mediums you are using to develop your ideas.

To really spell out the answer to the question of what tool I find most helpful to plan my game it is: the main medium I will be developing and presenting my ideas in, in this case: the game engine ?

Woops, yes what I put in parenthesis didn't make any sense and made it sound like I misunderstood what you suggested as project planning instead of prototyping. Clearly didn't proof read my rambling close enough, I've edited it out of my response.Thanks for the further clarity @Tom Sloper,