Welcome to the start of an incredible journey!!
React just comprises the application hosting the Babylon.js framework and WebGXX renderer - @Foxhoundn is wise to suggest taking on one at a time.
Unless you’re building a web application which involves 3D rendering (like a product catalog) that involves heavy HTML-to-canvas integration, you’ll spend most of your time looking at stuff in only one of these different “worlds”.
There is a TypeScript starter repository that the BJS team informally maintains - see this thread for more BabylonJS boilerplate for start project with TypeScrpit