Most package managers allow you to specify a dependency on Python 3, so you shouldn't even need to tell your customers. Otherwise, you can always use virtualenv and ship Python with your code.
And yes, if you're targeting Debian or Debian-like systems, make a deb. It's really not that hard, especially with newer tools like fpm.
Thank you for mentioning fpm, I'd never heard of it and often wished for something like it. Commenting to bring attention to it, and so I don't forget!
And yes, if you're targeting Debian or Debian-like systems, make a deb. It's really not that hard, especially with newer tools like fpm.