Plan to be around Tomorrowland, and Fantasyland once the fireworks are over and everything is open again in there. Anything fronting the Rivers of America is going to be packed, especially NOS and Frontierland. You could be up in Critter Country, too, but there's not as much to do-- Splash and Winnie, and maybe HMH if you have a FP for it (cause it's likely to have a long wait in the evening, Fantasmic or not). And you have to get through the masses around ROA, first, to get there.
Lines are usually better in Tomorrowland during F! and the fireworks, but I would still plan to collect FPs in the morning and use them on the FP rides, if needed.
If you wanted to see F! you could use the strategy of hanging around up in Critter Country during the first show, and the fireworks (which are viewable from the ROA location and many people stay after F! to watch them there) and then sweeping back down into the ROA area after the fireworks are over and most people are leaving in the opposite direction. Then you should be able to snag a good seat for the 10:30 F! show and not have to wait more than about 35-40 minutes.
I'm just speculating on all this, though. Who knows what the crowds will be like-- could be crazy for the first night of F!, could be not bad.
