This is a really ambitious project that has no guarantees. This game is all about creating an amazing experience for the next generation. I want to give them the same amazing experience that I had with games that I grew up with.
Hi. I was hoping to offer some advice, as many years ago I came to these forums announcing a RPG project of my own (that I continue working on). It sounds like you are new to game development (apologies if I'm mistaken), so I wanted to give you some recommendations based on my own experience.
1) Start Small and Expand
Even simple 2D RPGs take A LOT of time and effort to build. I know this better than most anyone. Our team originally had planned to develop the first chapter of the game and release in an episodic model. Well, even what we wanted to do in that first chapter turned out to be too complicated. Instead, what we ended up doing was to first make a "tech demo" demonstrating basic gameplay. From there, we produced a few different "mini RPGs" that had a playtime of 20-30 minutes. Only after we had been able to get this far did we have most of the necessary technology and content to really begin producing our final product.
2) Don't Create from Scratch
Specifically, I'm speaking about building your engine from scratch. We decided to do that (or rather, we were so damn ignorant we didn't even realize that using an existing engine was a viable option) and we spent our first two years mostly doing engine development as a result, instead of working on the game itself. Building your own engine will give you a better learning experience, but that's about the only real benefit for a small part-time team. I'd also recommend using freely available assets (legally) from sources like opengameart.org starting out. Trying to create all your artwork from scratch, especially if you are relying entirely on unpaid work, is very, very difficult even if your project is popular. You can always replace shared/placeholder art with custom made art later.
3) Don't Over-design Upfront
In my project's beginning, we spent the first few weeks nailing down every minor detail of features we wanted to see in the game before we really got started. This was somewhat of a mistake for a couple reasons. First, we were nowhere near ready to implement most of the features we desired to have. Second, by the time we were ready to implement the features, those early team members had all been replaced by new ones, who weren't completely sold on the ideas of the past team. As a result, we questioned whether a lot of those old ideas made sense, and ended up throwing out or replacing several of them.
It's good to have a general "loose" design starting up so that you are all on the same page though. I'd hash out the major features you want the game to have first with your team, and worry about the details later once you have a playable demo up and running.
Hope that helps you out. Good luck!