Wow, if you have reservations, you're ahead of the game!
For Fantasmic, do you have the early show or the late show? If it is the early show, when it is over, you can watch fireworks immediately afterwards from your same seat. Projections will be on the water in Rivers of America and fireworks will be towards the right side.
This is obviously not the best picture, but you can see the smoke from the fireworks relative to the center of Tom Sawyer's island (where Fantasmic takes place and the projections will be).
The WOC night it will be difficult to get into DL for projections. If you hustle as soon as WOC is over, you can make it to Main Street, but for someone who hasn't been before, it probably isn't worth it. If you go to Pixar Pier after WOC, you can see the fireworks in the distance without music or projections. DCA is really pretty at night, especially Cars Land. You might spend some time taking it in.
Edit: Just read that you have the 2nd WOC dessert party, not the first. You won't have time to check in for WOC (select your table), go to see fireworks, and return to line up for your show.
The third night you can view fireworks from Galaxy's Edge just past the Millennium Falcon