Doors and hatches..

Usually just some. However I've been know to replace all (gets expensive though). I'll also add some where I know a kit left some off. Like on ships I served on, or can be seen in photo's.

I'm trying to answer this question myself while doing my first 1/350 scale battleship. Finding correct references can be daunting since so many plans kinda scimp on these details. Pictures are a good resource, but now I'm finding myself trying to keep track of which porthole goes where while looking at a bunch of black and white, faded, pictures. I think from now on, unless it's going to the Admiralty and they are going to build a 1:1 scale from my model, I' m going just to put on enough doors and portholes to make the model look "scale".

I'll enjoy building it more.

Scott

I'll typically add PE details if a.) the detail is bad, or b.) is not where they're supposed to be.

Depending upon the ship (and scale) you're modeling, getting a set of builder's plans is not a bad idea, provided they match the time frame of the model.

Jeff