I did the Plaza Garden View Party solo in March when it was still Wishes. My party started at 7:45 pm on a very crowded Saturday. I arrived at the entrance, which was on the side where the Plaza restaurant is, around 7:00 pm and there really wasn't a line. There were people milling around but no actual line. I ended up sitting on a planter for a bit and then they started letting us into the party at 7:15 pm. I ended up being one of the first in the party area which is the top section near the ordering stations for the Tomorrowland Terrace Quick Service. The area did fill up some but was never crowded. I left there about a 1/2 hour before Wishes and found an excellent spot in the Plaza Garden. Despite the huge crowds that day, the Garden area was never crowded. I loved the party so much that I booked it again for January to see HEA for the first time. I'm guessing it may be a bit more crowded this next time since it's a new show.
Here's some links to the posts in my TR where I posted pictures from the party.
Wishes Dessert Party Part 1
Wishes Dessert Party Part 2