Don't stress over the FastPasses, you don't need to worry about those until you are 60 days out....so by your timeline, you have a few months to research and ask about it.
That said, doing the math, it looks like even if you went in October, you are within the 180 day booking window, so you will have to roll the dice. But don't worry, there is a lot of great restaurants and locations to eat at.
When you say "Nicer" are you talking ultra fine dining like
Victoria & Albert's or just crowd favorites like
O'Hana?
there is no secret formula or trick, other then if its not available, just keep trying each day or every other day. People cancel all the time. There are also message boards like this where people will post when they will be dropping their reservations.
List your location priority and be flexible. In the end, go and have fun. Generally, the food is not all super-elite level. But each place has their own atmosphere and that's why you are there—and for that, there are plenty of locations with great atmosphere.
On the flip side, they have recently added a
whole slew of new themed locations in Disney Springs (formerly Downtow Disney) and with a 19 year old, you might enjoy those better then a character meal with a bunch of toddlers. Some of these places will accept their own reservations outside of the Disney system, so you may try them directly.