Yes, once you fully catch up with the current story, you can visit the gallery on that save. The game will directly tell you how to find it once you reach that point.
Gallery unlocks are shared between saves, so if you missed anything, you can do it on an earlier save and it will unlock immediately.
(There are hints in the gallery.)
I wouldn’t recommend going for the porn out of context, as much of it doesn’t make as much sense (read: isn’t as hot) when removed from the story.