Yes, you can use both normal Windows 10 and the Insider Program under the same license.
Yes, you can use both normal Windows 10 and the Insider Program under the same license.
Yes, you can install both the standard Windows 10 edition and the Insider Program on your system using the same license.
This choice wasn't reliable for me. I had to reinstall it several times, possibly because of a time-limited option that lets you downgrade like a regular Windows 10 upgrade—after that point you can't revert.