Yes, it looks like Calva has first-class support for launching REPLs from your project, or for attaching itself to a REPL session that was launched in some other way: https://calva.io/connect/

Yes, you can. It's all pretty seamless with Calva & VS Code.

I can confirm that, Calva enabled me to get comfortable enough with the whole ecosystem to actually start with experimental projects.

I fully plan on making it my main language for my own projects, with that being Java and the web stack at the moment.