Umm Kulthum
Yes. Umm Kulthum is a historically attested name used by women in early Islamic sources; one prominent bearer was a daughter of the Prophet Muhammad. The name also occurs for other women in classical literature.
No. The specific name/kunya Umm Kulthum is not recorded in the Quranic text; knowledge of bearers comes from seerah and biographical works.
Literally 'mother of Kulthum' (أم كلثوم). In classical descriptive usage, Kulthum is associated with a full or rounded face, so the compound is sometimes interpreted with that nuance.
Yes—though historically it functions as a kunya, it has been used as a proper feminine name. It carries strong historical and familial resonance, especially among those who value connections to the Prophet's household.
Yes. Variants include Umm Kulsum and regional pronunciations that affect vowel quality; the Arabic spelling أم كلثوم is standard.