Hi, A Duck;
As far as artwork goes since the game will be 3d Voxel it will have a look / feel similar to that of minecraft. I'm trying to get license permission to use SapixCraft for the majority of the base materials and things since he has put such a massive amount of work into artwork for voxel based games. (I will use it for place holder art in the mean time, where applicable My understanding is that the voxel engine I'm using for unity "Voxel Play 2 | Game Toolkits | Unity Asset Store" shouldn't have an issue with 512px images but realisitcally I'm more about adding features than artwork so I'm leaning towards 32px artwork. I think it adds a good amount to the ability to texture over 16x