The engine is up to you, me personally because I cant learn how to code normally I use Construct 3 but also Gdevelop is about the same and 100% free.
Of course! I started out using my schools $20 cromebook lmao
That will be decided mainly by the engine you choose, although I have heard Lua is very easy.
https://www.piskelapp.com This is what I started out and still use, I also use Aseprite but Piskel works just the same for free with less features
Whenever one of my projects is failing I always think of what I learned from the project and not how it came out, even your worst most unplayable games are a learning experience.
Also one other tip that I can give is try to create easy systems for adding new things, like for instance if you have a bunch of weapon ideas don't add them all at once. Add one and then write the code in a way that you can either reuse it or copy and paste it for the other weapons instead of manually adding them all