Not overly easy, but do-able.
Looks like you’ve completed step one, use the
generate_fontawesome_essentials filter to only load the icons GP needs.
Next, you would have to use a tool like Fontello or IcoMoon to build your font file only with the 5 icons you need.
Those tools will give you font files.
You’ll then need to upload those font files into your child theme.
Now that you have that done, you’ll need to use @font-face to incorporate them into the theme: https://css-tricks.com/snippets/css/using-font-face/
Whichever tool you use will also give you a style.css file – you’ll want to copy that CSS and add it to your child theme as well.
Hopefully this is enough to get you started 🙂