There's no need to register an account with Ubuntu at all. You have no idea what you're talking about. You don't need a pro license to get updates for an LTS for 5 years of support. The "base packages" are both the "main" and "restricted" repositories - it isn't just a few "core libraries" as you seem to think.
Debian is an excellent distro but I can't even find out what Debian considers to be covered by their LTS. Their page about it is very vague. I would guess that it's the same though - "main" repository is what they cover. Similar to Ubuntu.