No.
Story scenes are not repeatable. (for obvious reasons)
Most other scenes are repeatable ... until a milestone in the story replaces them with a spicier version.
No.
The "gallery", is not a gallery in the usual sense.
It's just a (big) showcase of the animation loops. There's no scene, no dialog, no nothing, just the animation loops.
If you had played the game beyond the prologue, you'd know that already.
There's only one way to see a scene again without replaying the game ... reload a save.
Saves are free. Saves are unlimited. Saves are love. Save, save, save.