What size are the maps you're trying to create? The slider in the export option goes way too far for texture sizes. I would say a 2048 pixels resolution should be enough. Also, if there is no transparency in your materials, don't create an alpha map. The bump map can be generated from the colour map in another software, so maybe you just need to create the colour map, and those who will use your model will connect the colour map to the bump channel themselves, if you explain them to in a readme file.