Pavel sent me a request for a video on how to create pixel perfect textures and models. The models aren't technically pixel perfect, but they are aligned to a grid, giving them a very voxeley look, which fits well with Minetest and other voxel based games.
To achieve this all you have to do is hold down the Ctrl key while moving faces or edges to snap them to the grid. If you need to change the size of the model once it is created it is as simple as scaling the object up or down to fit your required size. If you are going to use the model as an entity you don't even need to worry about the size too much as you can change the size with your entity code.