No, there are too many external dependencies needed (specifically, you have to have installed all the dependencies you’d need to build it yourself, so we suggest just building yourself - then you’ll also have sources accessible for debugging CPython, which is the only reason you’d want debug binaries).
Depending on your build backend, you should be able to get it to build debug binaries for your extension while linking to a release CPython. If you aren’t planning to debug into CPython, this is just fine (arguably better) - as I said above, if you are planning to debug into CPython, better to build it yourself.
You mean --target? If so, then yes, this is one of the intended uses (though not as interesting as “downloading to bundle/embed”, IMHO, since eventually I’d hope build machines will just have what you need, or not be sensitive to user-wide installs, at which point a simple py exec -<version> ... to install/run on demand should be the norm).