OK you seem to have 3 questions here:
1) IRIS or Caché: If you're working with new the answer is IRIS. IRIS is our "latest and best" and you'll be best off going there.
2) Which IDE: Doesn't matter. Atelier is an Eclipse based IDE, which is nice if you're used to Eclipse. I haven't touched VSCode so I can't speak for that. Studio is our home-grown IDE. Choose one, I'm not sure it matters at all, as long as you're comfortable using it.
3) How to deploy: In IRIS we have containers for deployment, so if you want to go that direction, great. However, you might be more comfortable working on your own machine, which you can also do and bring in containerization later (if it makes sense). Remember, using containers is a tool, and it's not ALWAYS the right tool for the job.
Good luck! And if you have questions about building your application be sure to let us know!