For our family, we will only go to the second showing of F!. I would never wait that long for the first showing.
As a PP stated, if you can swoop in after the fireworks, you can find a great seat with only having to wait maybe 30-40 minutes. We usually watch the fireworks at 9:25 on Main Street, and then head against the masses into Frontierland to get to the river and have never had a problem. There are going to be CMs out directing traffic and if you can just follow the path where they are telling you to go then it shouldn't be to bad. Moving with the traffic flow in that direction is not as bad as trying to move OUT of that area. Everyone from the first F! and fireworks are clogging Main Street and that is the place you are heading away from. DH and I each have one of our kids in a stroller and make a plan to meet somewhere in case we get separated along the way. Works great for us!
When getting a place for the fireworks, we try to position ourselves to the left hand side of the hub closest to Adventureland and Frontierland to aid in our route after the fireworks are over. And if you do decide to do the nighttime entertainment on different nights, just know that you should try for the fireworks early on in the trip (the first night) as they have been known to get cancelled due to the winds at higher elevations.