First of all, let me tell you that I'm so looking forward to play your game! I love the source material, and had been wondering for some time why nobody was doing a proper homage, getting rid of some of the limitations of the era. I also love the low poly aesthetic; I'm so looking forward for it to enjoy a new revival similar to that of the pixel art.
About your situation, and that the development of your game, perhaps knowing of other experiences will help you, so here's mine.
I've been working on a game for a couple of years, without much previous, direct, experience.
One important thing is, I'm not working on it alone. Though I'm the one doing the programming, and learning along the way how to make it possible.
Early on I realized that my vision was overly ambitious, so the scope of the game has been scaled down several times. We're on the third devolution, and it's a drastically different and way simpler game. But we choose to keep things in the design that will help when/if we tackle the more ambitious game.
I guess what I want to say is, both managing the "size" of the challenge, and having a team (in my case, a friend), can get a long way to keep you working and keep going on.
Being realistic about what can be achieved, is a must. Otherwise what awaits is failure.
And I don't, I wouldn't feel ashamed of copying or cloning already invented game mechanics. As they say, you can only break the rules you know. It's all part of a process, and we all start imitating before we're ready to innovate.
There's another issue which be will be fighting soon enough, when most of the mechanics are in place, which is content creation. I would say the two most critical and harder to nail are both story and level design.
But here's an idea: Maybe with original characters, and a free level design tool, people can make their own story, and play their own game. Sure, I'd prefer to make my own game, batteries included, but if I manage to get that done, and I can't manage to create all the content I'd like to, I would still consider it a success!
Keep that in mind, whenever you don't feel like working on the game. Personally, as a programmer, I think working on other, related stuff, such as game tools, helps a lot. I'm not strictly working on the game, but I'm working for the game, which is still progress :)