I see you're going "smooth side out" on the OSB. I think I do it the other way but on walls, it doesn't matter as long as you're consistent so it doesn't show the different textures on the same wall (which may be hard to cover with paint).
Are you going to use plywood clips on the ceiling? I recall you had a pretty decent span between joists but was working on a solution to reduce the gap.
In the tack room I did not use plywood clips. It is only 8x8 so just two sheets. What I did was run a 2x4 parallel to the trusses. This cut the 4' span between the trusses to 2' and it also happened to fall right at the joint of the OSB. Since I'm able to put the screws right at the edges, I figured I won't need the clips. I've got one sheet up, I want to do the other one maybe tomorrow. I was able to get 4 sheets over last Friday. I put one sheet on the wall. One on the ceiling. Monica then used a sheet to cover a part of the metal in the barn area - after she miss-cut one and "ruined" it. Not a big deal, OSB is cheap and she was trying. How many women do you know that will run a circular saw?
Yep, we went with smooth side out on all of the OSB. If for not other reason, it catches less dirt - and believe me that is a concern in a barn with animals and a dirt floor. I believe we will paint the "exterior" walls of the milk room even though we haven't painted the rest of the OSB in the barn where the goats are. If it gets cold enough this weekend for the ground to freeze, I want to take more OSB to the barn. Right now with temps in the 50s (and some 60s) and tons of rain, we no longer have a solid base for a yard. In the good places it is more like a sponge or Jell-O. In other places it is more like Clam Chowder and you sink up to your knees. Makes it a little hard to get materials to the barn. If we had gravel it would help, but not really a good way to get a driveway there and normally not a lot of vehicle traffic will be going to the barn. A load of hay about every 5 weeks.