Measuring quality (narrow focus)
Item 5 ("English") edited.
As for the 2 sentence article, a baseline quality article that is very short might not need a separate introduction. That's a matter for the local community.
Maybe we don't mind a baseline article being short, so long as it's decent quality. Or maybe this means there are two levels of quality we can distinguish: - "baseline quality" (any length, even just 2 sentences, but has the key features as above) and then "expanded baseline article" (long enough to have sections and separate introduction). I think even the shortest and most obvious topic should have sources for its key facts, to satisfy baseline quality.
Who adds them and is tagging enough - separate question. I think tagging for sources is different from tagging for NPOV (which is why I put sources, verifiability, OR etc separate from NPOV). Users can sometimes argue for years about if it's neutral. So tagging and discussion may be reasonable. But it should be easy to require key or contentious facts to be sourced/verifiable/not OR. Hence why I categorized those two separately.