It's probably not "necessary," but that will depend on your goals. Weekend wait times are higher than weekdays, but that particular weekend is usually a fairly low crowd time, so wait times shouldn't be terrible. I'm pretty sure that weekend has early closures for the Orlando Informer meet up (private, separately ticketed evening event), so double check park hours.
Hagrid's and Velocicoaster don't have EP anyway, and are arguably the hot ticket rides. Are you focused on hitting the rides hard or are you planning to spend some time meandering and taking in the sights and entertainment? How much time will you take to eat? If you just have a few must-do rides, and want to see the shows and play with the interactive windows, etc., then EP won't help you there. If your focus is rides, EP will obviously get you through them faster, but you can probably get most of them done without EP. If you plan to ride "everything" AND stop to smell the roses and see the shows, you might have a hard time accomplishing that without EP. Actually, you might have a hard time accomplishing that even with EP. You need to be realistic about how much you can get done, and if it will ruin the day if you're rushing from one thing to another to check them off a list.
In my experience, the more people you have, the slower you move. Not because you walk slowly, but because you often have to negotiate the "what do we do next" - and inevitably different people will have different ideas. My advice would be to have a really solid plan, and stick to it. Part of you plan might include splitting up. You need to poll your group, and figure out what are the must-dos, what are the nice-to-dos, and what is skip-able. Where things overlap, do them as a group. Where they diverge, split up.