Wood – Which fence wood and paint/stain is this

I don't know about the cedar, but I built a screened porch a few years ago using standard PT lumber for posts and railings and painted it with a coat of primer and a coat of exterior latex pretty much as soon as it no longer appeared damp. Of course the 6X6 posts had been up and drying for a while at that point, probably 6 months or so. The railings were installed last and were probably only up for 2 or 3 weeks when they were painted. When we moved from that house earlier this year there were no problems with the paint, and that was after about 2 years.

Interestingly, the only paint-related issue we had was some peeling on the existing deck railings, about 4 years old and never painted at that point, that I painted at the same time to match the new railings around the porch. I have no idea what caused it, but I can say that I didn't prepare this older wood at all and it probably could have used at least a good pressure washing prior to painting.

To answer part 2 of your question.

You should probably reapply the stain a little earlier than the full 5 years - it could be starting to show signs of wear before then and you don't want to let the weather in.

If you are reapplying a stain then cleaning and lightly sanding the door should be preparation enough. If you want to apply a lighter stain then you will have to remove more of the old finish first.

Even if the stain does peel (which is unlikely) then sanding should be all you need to do. Be careful though to make sure that you sand the door evenly. If you take more off in one area than the rest it will show through.