Is there a recommended number for consuming black seed daily or only when ill, as reported from the Prophet (peace be upon him)?

Black seed is a medicine, not an act of worship, and its use should be referred to experts. No Prophetic tradition (hadith) has been reported describing how to use it or its quantity. Al-Bukhari reported from Ibn Abi Atiq a prescription for its use with drops of oil in the nose, and that Aisha heard the Prophet, peace be upon him, say: "Indeed, this black seed is a cure for every disease except death (al-saam)." And Al-Hafiz Ibn Hajar explained that this was for treating colds. Furthermore, Al-Tirmidhi narrated from Qatadah a prescription for "al-Shuneer" - black seed - with 21 seeds, but Al-Albani weakened its chain of narration. Al-Hafiz Ibn Hajar advised that black seed can be used individually or compounded, powdered or unpowdered, by eating, drinking, sniffing (as snuff), and as a compress. It is recommended to refer to medical experts for its proper use.