How fun!! We took my son when he was 4.5 months old for his first trip to WDW. We're DVC and seasoned pros, but the last time I was in the parks I was pregnant so our priorities were characters (for my son) and thrill rides (for me)! Everyone has had such great advice already, but I will add a few more:
1. Bring help! I could not have managed without my mom. It allowed my DH and I to go to
Jollywood nights and a re-planned date night at Citricos. Next time we go without her, we may hire a local babysitter for a day/night.
2. Put an AirTag on your stroller. We use a travel stroller and I had so much trouble finding it in the sea of behemoths in the stroller parking areas.
3. I would reconsider any meals that are buffets which sadly are most character meals. Perhaps at 16-17 months old it will be easier, but I didn't even make it to the buffet at Crystal Palace because I was focused on baby.
4. Schedule a Capture Your Moment photoshoot!! And do all the photo pass stops!!
5. I already can't recall if you noted the month you'll be there, but I highly highly recommend avoiding the summer season. It is HOT and I can't imagine doing that with a child. Everyone is already cranky from walking more than they're used to, being in a crowded theme park, and standing in lines for everything from rides to the bathroom, that I wouldn't recommend adding heat and humidity on top of it.
And finally, have so much fun!!