Hydrogen was released late in 2021 and I’m not sure how this changes the game.
Here is an article.
This is a good question. The answer may be both.
HTML, CSS, JS, React, Shopify platform, Shopify APIs, Liquid, GraphQL
$80 – $160k?
Shopify Headless CMS (Storefront API). Shopify plus starts at $2000 a month.
Not hosting within Shopify but hosted on separate server and embedding through an iframe.
What is Shopify Polaris? Design system is a set of comprehensive guidelines and principles that designers can use while building apps and channels for Shopify. It offers a range of resources and building elements like patterns, and is available to all Shopify partners…holds all the building blocks needed to create apps that will feel familiar to merchants, and won’t require a learning curve.
I think Polaris is a set of React components for you to use in your application so it feels like it was built inside of Shopify.
Also look into App Block and App Billing. Shopify has a POS System. Can use Webhooks.
In addition to above maybe some Apollo and Ruby on Rails