I think the "attacked by enemy when outside of view" comes from the characters hitbox being a bit larger than the sprite. We should have playtested it a bit more.
We could've looked into health restoration, yes. Maybe give you back some hearts when you go up a floor.
I'd recommend trying to limit how many enemies you fight at once to maybe 2, 3 at the most.
Gald you had fun with it at least :)