Basically all that. The unfinished part IMO is mostly for use in developer use cases, and that some ecosystems like JVM are not as well supported.
Can run yes, given that you have to spend some time learning Nix and NixOS specifics. I do that myself.
You either package the software if it is easy to do so—take a look a at nix-init which eases the process—or use Flatpack, containers, steam-run...
Just do it like me and listen to nature sounds like gentle rain.