I realize this is a new mod and all, but is there currently a way to craft the different kinds of terrain? Also, I think it would be cool to be able to put water in as maybe a reverse landfill :) just an idea of mine

You should be able to craft the extra landfill types the same way as crafting the base factorio grass landfill. Recipe is 20 stone -> 1 landfill.
There was an issue unlocking the new types if you added the mod to a game where landfill had already been researched. This is fixed in 0.0.2.

Good suggestion about the water, but it's a bit more tricky. Placing water under the player will kill the player instantly, and I'm not sure what to do about buildings. So no plans for placing water in the immediate future.

You could make a 3x3 area around the player that you can't fill with water, and as for buildings make a region similar to the concrete when around water, but opposite. That or make the water break buildings when its placed perhaps. I'm no modder though so I couldn't very easily say how hard either of those would be to pull off.