I think url design is largely unimportant for a blog because people don’t need to form those URLs the same way they would for some query frontend. The most complicated thing you might want to support is anchors/fragments.

There are other much more digestible ways to navigate a blog like RSS, XML, Google Search, the page that lists all your posts, clicking on tags. I think almost everyone follows links rather than editing the URL so the structure is kind of irrelevant.

They are supposedly important for SEO. I say "supposedly" because everything in SEO is speculative voodoo and no one (aside from the Google search team?) knows if it actually matters.

Yes. Maybe a little too much. Poorly design URLs are my pet peeve.

If I were building a CMS or a templating system for a blog then I might care about the structure for scalability and management reasons such as sharding of storage as part of the URL, programmatic global edits, etc... and that's assuming it might grow really big. Otherwise I don't think it matters that much aside from the potential voodoo wheresmycraisin mentioned.

YES