My idea would be 5 heroes.
Fire - Tahu
Wind - Lewa
Water - Gali
Onua - Earth
Now, I'm basing these on Var's idea of Earth.
However, the fifth one would be Pohatu, who would be a Toa of Stone/Rock. But I would reimagine the idea of Stone.
Now read me out.
The first four would be mentally very strong, as in they would be able to control their elements very well. But Pohatu would be physically super strong, like he was supposed to be in G1, while Onua in this new G3 would be stronger than the other 3, but not as strong as our big boy Pohatu.
Now, I'd like to talk about the designs/locations of the villages. Fire and Water are pretty self explanatory. Wind I'd say would be either on a tall mountain or in the tops of tall trees. Earth would be In a jungle - which, to add to it, could even be right below the Wind village, which would be in the trees above.
But what about the rock village?
Well, the Rock village would be at the foot of a mountain, let's say the foot of the volcano that Ta-Koro would be located on top of, so that's it's all close together and can be placed in reference to eachother. At the foot of the mountain, there'd be a big hole with a wall in front, and inside there'd be smelteries, crafter's shops and the like, as well as a large training grounds.
You see, the Po-Matorans, and in turn Pohatu, too, would be real big fans of 3 things - Strength, Honor and Glory. Of course, they would still honor the three virtues (if they were a part of the story), but these 3 would be their main focus.
So while the, let's say, elemental Toa could beat each other, given the circumstances, Pohatu could beat them through sheer strength and power of will. Tear down any vine, walk through any wind, brush away flame and swim against any current. He would be a personification of pure power, and his, and his matoran's, control of Rock would come purely from the fact that they're very strong.
Now, as far as evolutions of the characters go, I'd say they would gain a secondary power.
Tahu would gain Plasma
Gali would gain Ice
Lewa would gain Lightning
Onua would gain Psionics
Pohatu would gain Iron
The reason for all except for Onua and Pohatu are sort of obvious.
Now, Onua would gain Psionics because he would be mentally the strongest, and because of his control of Plantlife already needing a basis of Psionics. Pohatu would gain Iron because, according to him, that would be the next step in Strength. He would create armor and weapons out of Iron, he would bend it with his own hands, all to further his own power.
And if there was a villain, I'd say that they'd have the power of Light, rather than Dark. Why? Because they could consume/ingest Light while also producing it, which would make for a much different dynamic to how it was before.
I think I wrote too much.