I like it, maybe add a texture to the land and also maybe add wind. Good luck! :)

Don't use a text document, and don't bulk it up. I'd make is so each region (chunk of the world) use it's own file. This mean's you only have to load what you require. Plus I wouldn't use a text document, I'd recommend saving in a raw format which will save tons of space. To identify regions you could give them identification numbers which would vary upon their location within the 2D space for example: int regionId = (y / Region.SIZE) + ((x / Region.SIZE) << 8); I'd also recommend keeping the region size to the power of two. Best of luck. :)

Well for a start I would not store the whole world in memory. On start up make it build the world and save it in region based files. I'd then make it load only the region's within X distance. If an active region is no longer within view distance, it's destroyed and removed from active memory. If you don't understand me, just say and I'll make a quick prototype.

If you're still interested in this project I can teach you a few techniques on how to manage vast voxel worlds and still get a high FPS.