Right size base cap moulding?

My wife wants to add pine 1x8 shiplap board in the babies nursery ( to much HGTV Haha). We are looking to do the ceiling and one wall. I was thinking about using my 16 gauge finishing nailer to nail the boards, however on the ceiling there is 1/2 drywall. Will a 2 1/2 inch 16 gauge finishing nail hold the boards in the ceiling? I would have a bout 3/4" in the pine 1/2" in the drywall leaving just 1 1/4" in the ceiling joists. Maybe 3 nails per board at each joist? I'm guessing the wall will be ok but i'm just afraid of the weight of the boards on the nails. Any one have another options for me or will the 16 gauge nails work. Thank you.

I hope that I'm putting this post in the right place. I have a baluster that was split on our staircase, and I'm having the hardest time finding the pattern/model number online to match it to order a replacement. Does anyone know of what would be the best way to upload some images of either the broken one or ones currently in place, and find out what is the right line and model? Thank you, Andy