Hey, Alex from the PWA team on Chrome here.
My strongest advice to teams starting their journey now is to avoid legacy desktop frameworks (e.g. React) and to start with something that's modern-first (Preact, LitElement, Svelte, Vue, Stencil, etc.).
Each of those have good starter kits that I can recommend:
Preact CLI: https://github.com/preactjs/preact-cli
Polymer PSK (for LitELement apps): https://github.com/Polymer/pwa-starter-kit
Sapper (for Svelte): https://sapper.svelte.dev
Vue CLI plus the PWA plugin: https://www.npmjs.com/package/@vue/cli-plugin-pwa
Nuxt.js for Vue: https://nuxtjs.org/
Ionic PWA Starter Kit (for Stencil): https://ionicframework.com/pwa/toolkit
The reason we don't recommend React-based toolchains is their weight. I wish we had a good example of a React-ecosystem starter kit that was light enough, but thankfully some of the better ones can be used with Preact, e.g. Next.js supports Preact: https://github.com/zeit/next-plugins/tree/master/packages/next-preact
Whatever you go with, recommend you set a hard performance budget and automate conformance in your CI: