Plywood is lighter than osb, stiffer, grabs nails better, and is more resistant to water/moisture. It's going to be 2 months before it is covered, which means it's going to be exposed to any rain that falls. OSB is cheaper, which is probably why most builders go with it. OSB is made from younger tree's than plywood can be made from.
The plywood is structural. It makes fewer joints that are staggered, adding strength. This building is going up 3 floors, hopefully. Which means it's going to catch a lot of wind. And over 1000sq ft of roof means it can hold quite a bit of snow, first floor walls need to hold 2nd and 3rd floors, all their stuff, plus any snow, and take any wind gusts all at the same time.
Finished first floor plywood, ~60 nails per sheet, 8 per stud at 6" intervals, for 7 studs, extras along the bottom where the bottom plate is. Got all the bridging done as well. Every stud at the 5 foot mark.