The endings don't clash, you can in theory get the ending for every girl that has one in a single playthrough. I was considering some sort of strife, at least in specific situations, but opted against it in the end.
Some characters have a separate "bad end" (which just means that canonically the protagonist "retires" if they go through with those), but if I remember correctly I made it so you can check out most of those and then rewind back to the regular gameplay. Characters who have those might not be featured in the general ending, which I think makes sense.
Characters featured in the general ending (each with their own short, separate recap) are: Ariel, Kira, Beatrix, Lea, Dominique and Carla (I think Sonya and Eliza, the futanari, get mentioned too).
Characters with "bad ends" are Edith, Lady Pendleton and Eliza (there are more, but the others are all men, if I am not mistaken). I might have to add a scene for Edith in the general ending anyway, since it seems like she is the odd one out in this case.
If you mean the image gallery, it's in the menu. if you mean the replay gallery, sadly there isn't one. I didn't think to add it early on, and now there are just too many scenes. It's kind of long work to collect them, remove any code that might affect the path progression and make sure I am tracking the unlocks correctly.