I've heard they film the 1st weekend, too. But I also saw one or two posts saying it was filmed later in the month.
I figure if you just stay off Main Street and avoid the parade route when possible, it might not be too bad. The 4th is our 1st day there, too, and we HAVE to do MK first. We just do, it's a "thing".
We plan on being at the entrance 1 hr prior to opening, and have the UG 1 day adult plan at the ready. If it's not that crowded, great. But if so, we're prepared!