1.No, at best you get a shield when you beat the 3rd boss, which can be disabled by a fucking floating motherfucker who can stun lock your ass, make sure you have lots of MP or try to immediately get the Air screw ability which kinda trivializes said motherfuckers. Unless they managed to hit you.
2.Idk, but if you manage to beat the game, everything will immediately be unlocked in gallery.
3.Here have fun.
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Advice:Try to constantly save, never use the ressurect option which instantly revives you but you lose 50 Max HP. Get the 1st Red Skull near the 2nd boss, it gives lifesteal and severely helps early to late game, and kinda never level up your stats unless you've saved beforehand.
SPOILER ADVICE:
Use the spin attack against the final boss, if she shields up, run to the other side of the arena and slide under her, DON'T get raped by the machines, they can temporarily stunt your MP regen.