Want to make a top down shooter game

So the game I want to make is a top down, air combat game like 1942 or 1943 for the NES (screen continuously scrolls down as you move your plane around, enemies fly in or appear on the ground). It would use modern aircraft though. Already have my own aircraft and terrain tile sprites made.
The main points of it would be:

  • Can use 2 (or maybe 3) different weapons (gun with infinite ammo, bombs and missiles with limited amount)
  • Can use different aircraft (incl. different paint schemes)
  • Brief, non animated cutscenes between missions
  • Enemies fire back (their missiles can be dodged or thrown off by a flare)
  • Music/ SFX

It would also be nice to have these:

  • Additional aircraft/paint schemes that can be unlocked by finishing missions
  • boss battle (aircraft or ship that requires numerous hits to shoot down)
  • Friendly AI aircraft that fly by at the end of, or during a mission
  • missiles that can target 4 targets at once
  • Save/continue option (incl. redoing missions after unlocking all aircraft)

Here’s an example of the sprites and what I envision the game looking like:

My problem is putting all of this stuff together. I didn’t find any tutorials for anything like this, so which ones/templates would I need?

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.

my advice is start learning first. you will find many answers if you search.