[Cherryville Chuck]

OSB has a coating on the outside to make it somewhat water resistant. I read that the makers had to do this because the first batches which didn't have it couldn't survive rain which might occur before roofing went on. It should be fine. I put it on the inside of my shop for the same reasons as you. I didn't want drywall because it's too easy to damage. Once painted white it reflects light fairly well. It's more desert like where I am and I have about R38 in top of it and my shop stays cool during the day and warm in winter.

 

[Cherryville Chuck]

I think I just used a paint that didn't need a primer and a medium or long nap roller and 2 coats. Like Tom said, you get the added benefit of being able to hang a lot of stuff. I still put in sections of pegboard and painted it white too. It's way easier to find a lot of tools that way. Good for things like small squares, saws, hammers, and with the right holders things like chisels and screwdrivers. For long stuff like levels and yardsticks it's finishing nails in the OSB.

 

[Cherryville Chuck]

My shop got a lot brighter with the white paint but it also made a nicer place to work in.

 

[Cherryville Chuck]

Steve is correct about wire size. If the panel has a 20 amp breaker then you must use 12 gauge wire. It's a good idea to mix some plugs and some lights together in circuits or use dedicated lighting circuits. The last thing you want is for all the lights to go out if you overload a circuit.