Oh yeah, its going to be insane alright! And yeah because other people will be there at opening, its going to make the FP and the queue already filled at opening! Same time though, this stuff balances itself out after the few first chaotic weeks. Star Tours 2 had the same problem its first few weeks and FP were gone before noon basically. But by August, even with the MM people, the FP line was nonexistant in the mornings.
But I have a small story I can relate to of early FP morning madness, but in a different Disney theme park. It was Tokyo DisneySea when TOT there just opened in 2007, maybe a few weeks after opening. I showed up at 9 a.m., one hour before the park opened that day! The line was huuuuuuge! Its generally huge anytime in the busy season, but I mean long! It took me 45 mins just to get my ticket, an hour before the park opened.
Anyway, the park opened and I kid you not 95% of the people were all going to the same place. NOT to TOT, but to the FP line lol. I saw the looooong line forming ahead of me thinking people were lining up for the ride when I realized I was just in the FP line lol. The actual ride was only about 20 mins then (5 mins after the park opened though), but we ALL had the same idea! It took me about 20 mins to get the FP, lines were moving swiftly, for a 230 p.m. return time, but same length I couldve rode the ride already lol. The queue was already an hour by the time I got the FP, which I was still not bad and so just got in line with my 230 p.m. FP for later. But the crazy thing was after I rode it my second time with my FP, they still had FPs past 8 p.m. so I grabbed another one and rode it 3 times that day!
So sometimes it SEEMS really bad at opening, but stuff dies down! In fact, I probably shouldve just rode the ride first and got the FP later, but you are so afraid its going to be gone the first few hours of the day, you just get in line like the others!