In prior years, opening weekend was always tough to get all the mazes done without Express -- however, I would MAYBE miss ONE at most. Keep in mind, I always did like a 45-60 minute dinner so my friends don't complain, so if you could swing not doing a dinner, you'd be fine. The weekends after opening, honestly, were much easier. It's the hardcore fans of the opening weekend that create swells because they know the secrets that make seeing the event a bit harder. Other weekends, droves of people aren't even showing up until 8-9pm.
This year, with two shows, I can't imagine being able to see everything. If I were GA this year, I'd prioritize everything but Holidayz and maybe the Blumhouse show. Everything else I imagine should be fairly attainable with Early Access.
Just stick to a solid game plan, skip as many stops as possible, don't do any rides. Another trick is feel free to come back to an area later if the line has swelled up. Last year, on my second go, I realized doing Weeknd first was a trap and I instead switched it to last. Made everything way easier. Yes, going down to the lower lot twice sucks, but getting everything done - and done EARLY at that - is a godsend.