I don't remember for sure, I think I used about a half gallon per hull including waste. I sanded a lot of it off
Rolling seemed good for getting the thickness, but doesn't let you blend the edges. I was surprised that the new white was quite different than the boat white.
I wonder if it is the kind of sandpaper. does your palm sander have the vacuum holes?
I bought a box of discs and as soon as the paper got "streaks" of gel, I changed it out. I tried using a rubber stick to clean the disc, but quickly decided it was better to just toss them.
I'm not sure why it is so tough on your boat, but I didn't have to deal with thick orange peel either.
My surface was not super smooth when it dried, and I was a bit worried, but it really did go smooth fast.
Rubbing it down with higher grit wet went really well, and was very rewarding as it got more and more shine.
I was hoping someone else would help with more ideas.
Sorry you are having such a frustrating go of it.
You might think about just waxing it up and going sailing. As long as you have gel covering it, it won't hurt the boat. Work on it in the winter...