The answers to your questions are as follows:
1. The quantity and quality of a number of Muslims who are sufficient for the advent of Mahdi peace be upon him is subject to some variables, but it is understood from some statements by his honor Mansoor may God protect him that the gathering of ten thousand people for him can be sufficient; as he said in a message to a group of Mahdi-loving young people who asked him for guidance:
“Say hello to them and tell them: When everyone is turning to the right and to the left, you stand on the path of the middle, and when everyone is moving towards Zayd and Amr, you turn towards Mahdi. Remember God a lot and make heaven your goal and perform the prayer at the earliest time and pay Zakat to its people and do good to your parents that you will not stay with them for a long time and promote what is good and forbid what is evil and lighten your work and leave everything that can be left and take everything that can be taken and get ready to move to Mahdi; because whenever I find enough helpers, I will move towards him, even if there are seven seas between me and him. Who will guarantee me ten thousand people so that I can guarantee the advent of Mahdi for him?! The Earth is rotting and the time is like a festering boil that is open, but the future will belong to the pious”.
Of course, it seems that his honor’s intention from this “ten thousand people” is those who have been trained and educated in his presence with firm faith in the path and method and ideal of this noble man, and have acquired the necessary scientific, moral and martial readiness to help Mahdi, not those like you who only agree with the thoughts of this noble man and respect him; as he wrote in a letter to his helpers:
“You think it is enough for you to consider yourself my helpers and do not follow me in practice? How can I revolt with you while you are so unreliable?! Where are my true helpers? Where are those who, like Christ, left the world behind and were freed from all its attachments? Where are those who were accompanied by death and saw God before them? They cried so loudly for the fear of fire as if they were mothers whose child is dead! They looked around the sky in such a way that you thought they could see angels everywhere! They worshiped God and refrained from worshiping Taughut. They obeyed their leader and surpassed each other in helping him. As if they were steel boards or soaring mountains! When they attacked the enemy in their ranks, it was as if they were launching a tornado and a sandstorm! They monitored their behavior and knew the time of each speech. They were adorned with moral virtues and descended from great vices. They were anonymous and unknown on earth and famous and well-known in the sky. The dust had settled on them and the color of their faces had faded. In the middle of the night, it was as if they were honey hives! They spent their time praying and repenting and reciting the Quran till the morning, and spent their time in science, jihad, and serving the people till the night. They were neither tired nor hesitant. God bless them. They spent their time and left. Now you are left for us. So try to be good successors for them and follow them and know that you will not see victory until you are like this”.
From this statement of his honor that said: “You will not see victory until you are like this”, it is understood that achieving this quality is necessary in addition to that quantity, and the gathering of ten thousand people without gathering all or most of these attributes is not enough. Therefore, in addition to gathering this number of people, his honor has set his mission to educate and train them for Mahdi; as he addressed them in a speech and said:
«أَیُّهَا النّاسُ! إِنَّكُمْ تُریدُونَ أَنْ تَقْتُلُوني كَما قَتَلْتُمُ الصّالِحینَ مِنْ قَبْلي فَلا تَفْعَلُوا فَإِنِّي وَاللّهِ لَو بَقِیتُ فِیكُمْ لَأَشْحَذَنَّ رِجالاً مِنْكُمْ شَحْذَ الْقَيْنِ النَّصْلَ! أَجْلِي بِالتَّنْزيلِ أَبْصَارَهُمْ وَ أَرْمِي بِالتَّفْسِيرِ فِي مَسامِعِهِمْ وَ أَسْقِیهِمْ كَأسَ الْحِكْمَةِ حَتَّى یَمْتَلِئُوا! أَلا إِنِّي أَخْتارُ خِیارَكُمْ لِلْمَهْدِيِّ كَما یَخْتارُ النَّحْلُ لِیَعْسُوبِها خِیارَ الْأَزاهِیر!»; “Oh people! Indeed, you want to kill me as you killed the righteous before me, so do not do this; for I swear by God, if I stay among you, I will temper some men among you, just as the blacksmith tempers the sword! With the revelation (Quran), I polish their eyes, and I pour (its) interpretation into their ears and I make them drink a cup of wisdom so that they may be filled! Be aware that I will choose your best for Mahdi, just as the bee selects the best flowers for its queen!”.
This is the meaning of preparing grounds for advent of Mahdi and the mission of Mansoor Hashemi Khorasani.
2. It is hereby understood that during the time of none of the previous caliphs, the mentioned quantity and quality have not been combined; in the sense that either ten thousand people did not gather to support the caliph of God on earth, or they have gathered but they did not have the minimum necessary attributes and therefore, they were examples of ﴿لَا يُسْمِنُ وَلَا يُغْنِي مِنْ جُوعٍ﴾. As with this basis, the flaw in your statistics from those who have been around the caliphs of the Messenger of God peace be upon him and his family becomes clear; because the lack of the least necessary attributes in them is known, and even famous; considering that the complaints of Ali ibn Abi Talib from the weakness and shortness of his helpers has been narrated in a Mutawatir way, and the disloyalty of Hassan ibn Ali’s helpers is one of the famous parts of history, and only seventy-two people remaining for Hussain ibn Ali is not hidden, and Abu Muslim Khorasani was an inviter from the Abbasids and his suggestion to Jafar ibn Muhammad was just a test to realize if he wanted to rule then he gets killed and would not have the opportunity to oppose the Abbasids, and for this reason, he faced a strong denial of his Excellency and the Safavid era -contrary to your strange idea- did not have an opportunity for advent of Mahdi, rather every disaster was during the Safavid period, and the Shia distortion reached its peak. Hence, many narrations from the Imams of Ahl al-Bayt have been narrated in which they have said that if they had a sufficient number of qualified helpers, they would revolt and it is clear that Mahdi peace be upon him is no different and therefore, if he obtains a sufficient number of qualified helpers, he will revolt, even in this case, revolt would be obligatory for him and abandoning the obligatory is a sin, and the Mahdi we know, is not a sinner.
3 and 4. And now, just like in the past, there is not sufficient number of qualified helpers for Mahdi, and if there is, they are scattered on Earth and therefore, they are not able to prepare grounds for advent of his Excellency; as the preparer for his Excellency, his honor Allamah Mansoor Hashemi Khorasani may God protect him has pointed to this unfortunate point in the noble book “Return to Islam” and has said:
“This is while the majority of Muslims, quest for rulers other than Mahdi and protect, support and obey them instead of him and there is no sufficient number of people among them to protect, support and obey Mahdi and even if sufficient number of people are among them for this task, they are separated and are spread around the world and it is clear that each of them alone and separate from others is not able to protect Mahdi’s safety and freedom and therefore, their union is essential for this purpose, while there is no one to unite them for this purpose and this is the reason for Mahdi’s non-advent, even as limited as mere access to him. On this very basis, I have been traveling for a while around the world, seeking for competent people, in order to gather a sufficient number of them and to make them ready to protect, support and obey Mahdi, so that when God sees their gathering and readiness, makes it easy for them to access Mahdi and paves the ground for his sovereignty, in order to be a preparation for his advent; regarding that if this matter is carried out today, he will definitely appear tomorrow, even access to him would be possible tonight; since God does not oppress anyone even for an hour; as God has said: ﴿فَإِذَا جَاءَ أَجَلُهُمْ لَا يَسْتَأْخِرُونَ سَاعَةً ۖ وَلَا يَسْتَقْدِمُونَ﴾; “So when their time comes, they do not delay for an hour and do not overtake” but yet, the more I have searched, the less I have found, to the extent that I have got tired and frustrated; because it seems that the world is empty of competent qualified people”!
This complaint of Mansoor Hashemi Khorasani is not dissimilar to the complaint of Ali ibn Abi Talib and the complaint of Hassan ibn Ali and the complaint of Hussain ibn Ali and the complaint of other Imams of the Ahl al-Bayt, but it is undoubtedly the continuation of the same complaint and therefore, we can say that there is no difference in the people of the current time; except that today’s people, unlike the people of the past, still have time and can learn from their weaknesses and shortcomings and make the necessary differences in themselves and this is enough for us to have hope and make efforts; especially considering that our task in any case is to prepare the grounds for sovereignty of Mahdi, even if it does not lead to any result; because what we can do is doing our responsibility, not to achieve a result, but it is fair to say that achieving such result is not possible except with the occult help of God, to the point that if the movement of his honor Mansoor is fruitful and a sufficient number of qualified helpers gather for Mahdi, there is still no hope for success of his honor until God sends down His angels to help him; as one of our companions informed us and said:
«سَمِعْتُ الْمَنْصُورَ یَقُولُ: لا یَخْرُجُ الْمَهْدِيُّ حَتَّى یَنْزِلَ الْمَلائِكَةُ وَ لا یَنْزِلُونَ حَتَّى یَجْتَمِعَ الْمُؤْمِنُونَ بِخُراسانَ وَ الْمُنافِقُونَ بِالشّام»; “I heard his honor Mansoor says: Mahdi will not reappear until the angels descend and they do not descend until the believers gather in Khorasan and the hypocrites gather in Sham”.
We ask God for success of the gathering the preparers of advent in Khorasan and for the angels to join them to help Mahdi, and we trust in His promises and good news.