Writing an epic story takes a lot of planning, and by epic I’m talking something that spans multiple novels, has scenes that take place all over the world in question (or even on multiple worlds, where applicable), and has more than one major event taking place at the same time. Telling such a story requires many things, not the least of which are lots of main characters.
Most stories have just the one Point of View (POV), because that’s all that’s usually needed. But for something epic, you’re gonna need a number of POVs, which means establishing several characters ahead of time to do the job. Why this need, you ask? Take something like the Civil War, or World War II. A whole lot of battle fronts and stuff going on all at once, and to make the reader feel for everyone involved, at each such event he needs at least one character he can identify with as the voice of that seen; a POV character. Any battle or event feels more personal if you have one guy in the field through whose eyes it is seen, rather than simply some generic overview from on high. So, early on in your epic, establish a number of characters as your first-line. They could all come from the same group, or at least interact somehow, but they should be well established personalities before they are needed. Then later as your plot develops and you find a need for one guy to go to the western front, while another has to sneak in to spy on the enemy battle plans, and yet a third is on a quest with a couple of friends to find the Mgic Gizmo that will make all the pain stop. Each of these requires a POV character to ensure that the reader will feel the import and emotion of the scene in question.
With multiple main characters, you don’t have to focus on just the ONE event, but display equal concern with everything going on. After all, this IS an epic, so you’re free to have a LOT of important events mixing it up. In fact, the bigger and more complicated the epic, the more characters you DO need to keep track of it all. So, don’t be afraid of breaking the rules and having a lot of main characters; it saves the ONE characters from having to be everywhere at once.