I also agree that a FP isn't necessary for this show. We've been to it a few times and have never missed a capacity cut-off.
The amphitheater does hold quite a few guests, but it's not a huge venue, so I don't think there are really any "bad" seats. That being said, I do have a tip for potential "extra magic" on your visit.
At the end of the stage show, Belle & the Prince give a child a rose from the stage. A CM picks the child before the show starts and the family is seated in a roped off row up front for easy stage access at the correct time. I've seen it stated before that people have been chosen while waiting at the beginning of the line, but for us, my daughter was chosen as we were walking up to the mostly full theater not long before show time. Specifically,
my advice would be to just keep your eyes out for a CM directing people up the outside walkway and is potentially holding a 3x5 card and a marker. That's the CM you want to make sure you smile at and say "hi" to

They'll talk to your child and then issue them a card that you take to a seating attendant CM who will escort you to the roped off seats. This is the card they personalized and the rose that was given at the end of the show:
Additionally, I think they might look for a child that look like they won't be too scared to go up to the stage since it's another CM that escorts them from your family seat and stands by them in front of the stage towards the end of the show. If you have a Disney special occasion pin for celebrating something on your trip, then have your child wear it as well. DHS is probably
the best park at wishing kids a "happy birthday, princess!" throughout the day when it's their birthday and they are wearing the pin and I think that's what initially caught the CMs attention to talk to my daughter.
Of course, none of that may really matter and it could just be completely random... but my thoughts are, it can't hurt to try

Hope you enjoy your trip!