Probably the largest (disk) part of creating a level will be the textures/art, if you have only one simple tileset then you will have little disk usage. You can use the same tileset for every map making it a small barrier to enter, then the level files are small while the art is big and seperate.
This is why I mentioned “Taking a seed and generating a level”, with generated levels you can give a “seed” to the program and it will create the same level every time. So if you distribute only the seed it will be extremely small.