Adalah – as a condition in the imam of the congregational prayer and in the witness – is a level of fearing Almighty Allah that leads to avoiding the committing of major sins. Committing small sins without insistence does not affect it.
Adalah – as a condition in the marja – is a high level of God-fearing which leads the person to refraining from disobeying the religious laws and committing sins – whether the sins are small or major. If on the rare occasion he commits a sin, he would rush to repent to Almighty Allah and seek his forgiveness.
A person who holds 'adālah is called "adil".

It can be determined by one of the following:
1. Knowledge and certainty that originates from dealing with him or from other ways of reaching such knowledge.
2. Testimony of two Adil witnesses.
3. Good apparent behavior.

Adalah is defined as not committing the big sins, and when committed the individual repents, and not repeatedly committing small sins.

The Adalah of the imam must be considered before one offers congregational prayer. It can be determined by knowledge and certainty that originates from dealing with him or from other ways of reaching such knowledge, testimony of two Adil witnesses and by good apparent behavior. Having a big crowd that offer the prayer behind a person is not sufficient.

There is no specific time for this, but it depends on socializing for a usual period that is sufficient for the manifestation of goodness from him and the absence of ill deeds.

The prayer behind a person whose Adalah is not established is void.

The prayer behind him is invalid unless the conditions of the Imam of the congregational prayers are met. Presenting himself to lead the congregational prayer by itself is not sufficient.

Your prayer behind such a person is invalid.

Adalah is a condition in the Imam of the congregational prayer, which is observing the religious laws and its boundaries. One of the main boundaries of the religion is precision in the religious aspects and not rushing into judging them.

The prayers behind such a person is not valid. If you doubt the Adalah of a person, the prayers behind him is invalid.

It is permissible to do so if such prayers cause closeness between the hearts. It is not permissible if this was for the sake of adulation. However, one should recite himself in the first two rak'as.

It is permissible to offer the prayers behind a Sunni imam if such prayers cause closeness between the hearts. It is not permissible to do so if this was for the sake of adulation. However, one should recite himself in the first two Raka'at (units).
If he hears the verse of prostration with them and they prostrate he can do so as well and his prayer will be in order.

His intention will not be offering congregational prayers.

If the Adil believer has committed a sin and it is known that he did it because of disobedience, then the prayer behind him is invalid, unless it is know that he repented to Almighty Allah from such a sin or he repented from committing all sins.
If it is probable that the believer had a religious excuse when he committed what appeared to be a sin, then his Adalah remains, for instance, when he backbites against a person and it is probable that the latter oppressed the believer or was openly committing that sin and similar reasons that justify such backbiting.

It is not permissible for him to present himself to lead the congregational prayer if he knows that he does not fulfil the requirements of the Imam of the prayer, in such a way he would be considered as cheating them.
If they asked him to lead the prayer, it is permissible to do so, although it is better not to in this particular case as well.
If he was praying alone and someone decided to pray behind him in congregation, then his prayer is in order and he has not committed a sin. If he was not qualified to lead the prayer, he should not apply the laws of the congregational prayer on him, for example, referring to the people praying behind him when he has doubts.

It is permissible for the person to lead the prayer after repenting to Almighty Allah and seeking His forgiveness.

If repentance was sincere then the attribute of Adalah is returned and one can follow him in the prayer.

Yes, it is permissible to lead the prayer in such a situation and it is permissible for others to pray behind him.

If the person offering the prayer behind the imam knows the correct recitation, then following him in the morning prayers or in the first two rak'as of the Maghrib and Isha prayers is invalid based on compulsory precaution.
If he is following the imam in the last two rak'as of the Maghrib and Isha then the prayer is valid. The prayer is also valid if the praying person and the imam make the same mistakes in the recitation. Following such an imam is also valid during the Dhuhr and Asr prayers if the praying person recites for himself.

If he pronounces the letters correctly, it is permissible to pray behind him.

Yes, he is allowed to lead, but whoever can recite better than him is not permitted to pray behind him based on compulsory precaution in the first two rak'as of the Maghrib and Isha prayers and during the Morning Prayer. Whoever can recite better can follow him in the Dhuhur and Asr prayers but he must recite for himself.