I wouldn't worry much about performance in your case. Just make the chunks small enough, and there won't even be a dent in the FPS when a new chunk is loaded. Try to aim for 16x16 chunks.
Thanks for your answer! Well, making the chunks small enough does work for this project, since I'm using a heightmap, but for my 3D-Cube-World, it lags the game down once in a while. What I'll try now is doing the loading in the free time between the render loop and the next execution of it.

I'm 14, too, started HTML/PHP at ~12, gave that up, started Java last year by modding Minecraft, started programming my own games since this year, did some stuff with network programming, started lwjgl 1 month before I turned 14 and have started a voxel engine since I'm about 14, too. This is truly astonishing..

