We had plans to fix and implement pretty much all the problems you mentioned, but we ran out of time. The boss was supposed to start with fewer projectiles and then increase as he lost health, to ease the player into the boss's mechanics. We also wanted an animation and sound to play when the boss is vulnerable, because right now it's pretty much impossible to tell. For the difficult settings, we didn't have time to properly playtest and tweak the settings, so they are just some numbers I thought would work; they did not.
Thanks for the in depth feedback.