Welcome, I like maps with satellite style and use some NASA imagery for some of this too. What you need to do is to make a map where parts of it are at different resolutions to other parts so that when you zoom into some of the areas then you have more resolution. Trying to have street level res for the whole world does indeed give you a real problem of vast bitmaps. Only Google seem able to manage to deal with it at that scale. So you need to manage multiple levels of detail of the same area and there are several software solutions to manage that for you.