Hi! You will have a great time.
First of all Grad Nights are a separate ticketed event and you can only attend if you are a senior attending a participating highschool or a chaperone of the participating high school. We were there last year during this time and it did not affect the daytime crowd level. You will not notice a thing.
What will you love about the PBH??? Everything. When we go to WDW we stay at the GF in the main building RPC (a basis of my comparison). You will find going to USO is a relaxing vacation with a great theme park attached to it. I love that when you leave the parks you feel like you are a million miles away from a "theme park". The rooms are huge & beautifully decorated. There are 2 pools within a close distance...the beach pool with a fun slide and the quite pool. Both with bar & food service. There is a Spa, great restaurants, bars and a beautiful outdoor venue. I also love the fact htat when you leave the theme park and go back to the hotel there is no sign of a theme park...no "mickey mouse" in your face kind of theming, except in the gift shops. Also there is plenty of time to enjoy this beautiful resort hotel because of FOTL access. There is no need to get up early. You can take your time, go on your favorite attractions many times and have plenty of time to go back to the resort and enjoy the pools. We suually get to the parks at 10am and are done by 3 ish, head back to the PBH go to the pool and relax before a great dinner somewhere. The food at USO in general is much better than WDW, not at the PBH but all over USO.
I love both WDW and USO, I just find USO to a much more enjoyable vacation and truly relaxing. We will be there on the 4/22 and go the same time every year. Low crowds and beautiful weather!