I fear you will not find a complete game as a template, where you just change the sprites and you are done.
but I can’t see any impracticable task on your wishlist.
you sholud put all of your player images in the different animations of the same object. you can change the animation of a sprite object any time.
using different weapons is a bit more tricky. I can’t remember how this is working in that type of games. you have two potions. enable two or three different weapons at the same time. this way you need more buttons. put the three weapons in to three different buttons, or keep one fire button and at least one button to change weapon. or, enable only one weapon at the same time and change the actual weapon type when the player take a power-up. In this case you should use the knowledge from the “state machine” tutorial.
you can learn how to use sounds in GDevelop. same the save/load function too.
ect…
my advice is start learning first. you will find many answers if you search.