@Brawn To try and answer your questions:
1. Yes. Repl.it has a built-in IDE that can work in Node.js, and you can access Discord in the browser (though I'd personally recommend to use the app).
2. I would say that a Discord bot is a great way to start programming. You'll be working with mostly discord.js' functions, which read very much like English, and only need to know things like if statements, and for loops.
As for Rust, I've never played it so I can't comment.
Hope this helped!