these are the config files for my project - not yours . i thought i show you my config and you can adapt it for your project though i have no rights (i’m not allowed to) to commit/push or to create a new branch in your project - so i can not make any changes to your project.
what i would do is: create a .gitpod.Dockerfile copy&paste the content of my .gitpod.Dockerfile (from one of the links i posted above) and change 14 to 16.9.1 (or whatever version you like to use)
adapt my config from my .gitpod.yml (especially line 2 for using the custom dockerfile), change line 14 to
npm run dev and change the port to 3000
i hope it’s helpfull