Not to discourage you, but you have to really think very hard about this, especially if you’re going it alone (or if there will only be a few people to help you). The truth is that the secret to getting good animation or VFX are established in two things:
- Good Pre-Production Testing
- Good Iteration Turnarounds.
Asset creation and Rendering are the two main “time drainers” and you are currently experiencing the former.
The thing is you can’t begin any testing, or hope to iterate any image sequences until you have the assets. The more assets there are, and the more complex they are, the tougher you will have it.
What I’m saying is, there will be MORE battles up ahead than just getting past making your organics. EACH one of them will have to be fine-tuned to a certain standard across the board, and that’s effort PER organic character. Not just when they’re standing still (ie: Modeling/Texturing) but more so when they are all in action.
And that does not count yet iterations you will have to make for editorial purposes (ie: “Does a scene not work?”, “Is this the right cut?”, “Is the pacing right?”)
All I’m saying is that you have to appreciate the entire scale of the mission to make this picture and you have to “pick your battles”.
Personally I’m not sure it’s worth it to force the number of characters. I’d go as far as to make a “Primer Story” rather than the main one - basically a “test bed story”… instead of the main one you want to do if it will help you gain experience.
No one has asked you this: But does this concept call for spoken dialogue? Because you have to note that at places like Blur, facial acting and spoken dialogue were the subject of an entire project in and of itself (ie: the Face Robot project). Also you have to note the short film LE GOUFFRE did not tackle spoken dialogue because it’s really a big leap.
Again: Pick how many enemy hordes you want to fight against in your “debut match”. 
You can always attack “the full monty” at a future time with what you learn from previous efforts.
That’s a question best answered by yourself: Will you be happy that all the characters have identical faces? Will this be a solution you can build on for the future, assuming the project is a success? Or is this really a solution you will discard later on?
Would you consider the possibility of spinning off a Mecha Episode as the first thing you do? Wouldn’t be the first time. Remember even George Lucas decided it was better to start STAR WARS with Episode 4.
Again, personally, I’d shy away from something as difficult as organics and a death scene for something so new. Especially if the scenes in question, to deliver some of the ideas you mentioned about Milton and the betrayal, require dramatics or spoken dialogue.
It’s not that it cannot be done. It’s just from the fact that you’re going it alone, and there’s so many things that have to be considered: VFX, Color Scripting, Animation, Render Benchmarking, Viewer Testing, Planning for Iteration Feedback Loops…
I just don’t think it’s the right idea to get caught up trying to win one foothold on a beachhead without regrouping first.
But, at the end of the day, it’s your concept. Just wanted to help.
Good luck. :arteest: