Here's what I think:
1. It sounds to me like you've been leaning towards doing this for a while, so I think if your mind is in it enough, definitely move forward with it. It might be an interesting idea to portray Bionicle characters as simply being human for a change.
2. This one seems to sound like it's the most popular so far, and it does seem like a good idea, but I'd be careful about getting lost in the actual expanse of the world you create. Take extreme care about not getting too convoluted with it, so that readers won't find it hard to come to grips with the story. (like me )
3. I think that this idea will be the best received by the forum in general. Anyone who read the first epic will probably end up reading the sequel, so this is the route to go for the most feedback, I'd say.
4. If you were to start up comissions again, I'd be willing to buy one this time.
Anyway, whichever one you pick, I'm certain it'll come out even better than most people expect. I'd say go with the one you think will be the easiest to handle amidst life stuff, so that way your project has the least chance of being put on hold. All in all, looking forward to what you'll come out with next.