As @rebeecky says, you absolutely should be able to get through everything in both locations of WWoHP. Whichever headliner you don’t do first will probably require you to wait in line for awhile. For example, if you arrive at USF at rope drop and do Gringotts, Ollivanders, and wander through Diagon Alley, by the time you take the HE to Hogsmeade, you’ll probably have to wait a bit for Forbidden Journey. With those crowd levels, it may only be 30-45 minutes, which isn’t too bad. Keep in mind that on-site guests will get into WWoHP an hour early at one or both of the parks, so that will affect your wait times a bit.
If I were you, I’d make a custom touring plan with just the Hogsmeade and Diagon Alley attractions and see what it tells you for waits, with and without EP. That will then help you decide if EP is worth the cost. You’ll have to make two separate ones and adjust the start and stop times. If you need help with that, there are lots of us who would be glad to assist!