Thanks for the harsh but useful criticism!
1) Indeed I completely forgot to remove it
2) There is an ammo counter on the top left. I figured the player wouldn't immediately be using the railgun until ~300m so that's where I placed that part of the tutorial. Guess I should trigger it earlier?
3) I could add that, these three points are enough to justify a v1.3. While I'm at it, how was the difficulty ramp-up (spawn rate, mob HP), too slow? Too linear?
4) This is however completely intended as StS is not a run and gun; knowing when to move and when to shoot is everything, which is why I specifically highlight this point in the tutorial and recommend the player to destroy projectiles coming from the front with their sword.
5) Can you be more specific?
6) 
^This is what I expect you to click on ;)
(This screen + the 2$ suggestion are itch's default thing)
If this really does bother you, I've deactivated the prompt.
Now don't forget that this is a jam game, made solo in three days, from scratch. Making something even remotely decent with such a scope is extremely difficult.