We have a covered walkway between our garage and our house with the lower half of the walls being brick and the top half wood framing that was used for storm windows. We've removed the storm windows, may add screen at some point. Some of the paint on the wood framing is starting to peel and flake and expose wood beneath. So, time to sand, clean and paint.

My questions -
1. where the paint seems ok (no cracking or peeling), do I need to sand this down to bare wood or just sand enough to remove loose paint and smooth edges?

2. if I don't have to remove all the old paint, do I use an (oil based?) primer only where bare wood is showing? or over the whole area?

Thanks!