I would encourage you to not skimp on the painting, particularly the primer for this situation. I deal with the aftermath of builders using the cheapest material and labor possible for painting houses, inside and out, pretty regularly. do it right the first time and you'll be glad you did 10 years from now, 20 years from now. use the best quality stain killing primer meant for use on exterior bare wood that you can lay your hands on. getting that bare wall made of glued together wood chips sealed properly will make a big difference over the long haul. I'd suggest topcoating with high quality exterior flat or satin house paint, depending on whether or not you'll ever want or need to wash the walls. satin will be more washable and have a higher light reflective value than flat.