Is a specific public opinion required if the Hizb takes the ruling, and is not required if the Khilafah is declared by someone else?

May Allah reward you on our behalf with all the best and may Allah grant Islam and Muslims the victory, by your hands. My question is: Is carrying the Dawah an obligation of sufficiency or an individual obligation? Does carrying the Dawah with the group is similar to carrying the Dawah as an individual?

Could you also explain to us regarding the opinion of Abu Hanifa, Sufyan al-Thawri and others that there is no Riba (usury) in Dar ul-Kufr inferring the hadith (There is no Riba between a Muslim and a harbi in Dar al-Harb) and the evidence that Al-Abbas dealt with usury in Dar ul-Kufr and also arguing that Abu Bakr bet the polytheists in Mecca and the Messenger (saw) supported him, is…

Some people say the Hizb will be working like in the third stage, and some people say that when the transition to power ends, the third stage ends and the party begins a completely new work, which is holding the rulers accountable and guardianship of society... Which statement is correct and more likely true?