Firstly, the standard library will compile to Wasm32 for the most part. There are a few small features that do not work (pointers for instance) but you can include any of the libraries in the core of rust in your wasm project with bindgen. (You can also include many of the 3rd party libraries as well.)
You can create a monorepo with bindgen and not reference any JS functions.
From what I know you can't fully make a webcomponent in wasm-bindgen, but there are alternatives that do allow for this.