There is Calva for VS Code but the community default is emacs and cider

Emacs isn’t required. You can always create a REPL plugin. Emacs just does a lot of heavy lifting for you due to comint, sexp navigation, and process management being included.

building your own library from scratch instead of contributing to a standard library

Simple data structures lead to very generic function. You don’t have to write tower or massive spread of abstractions like in Java or TypeScript. A struct is nothing than a hashmap that can help a typechecker. Most lisp programs prefer primitives or functions instead of manipulating complex objects -never ‘buffer.name’ but ‘(get-buffer-name buffer)’-.

From a module, what you need are functions and an opaque state holder.

With such philosophy, you don’t need a lot of libraries, which are often designed to be complex, when you need a simple model.

Third one you need to mutate it a little bit

You don’t. Clojure already does the optimization for you for the standard data structures, and they are the only things you need in most cases.