Although all the details of Islamic rulings need to be sought in the risalahs of the maraje’, nevertheless, generally speaking, according to the Ahlul-Bayt, the sacrifice made on Eidul-Ad’ha (the Eid of sacrifice) can be divided into two categories:

1- Mustahabb Sacrifice: The sacrifice that can be offered by all Muslims, regardless of them being in Makkah or another city, and will be rewarded for by Allah (swt).

2- Wajib Sacrifice: One who has become muhrim (entered the state of ihram) for the Tamattu’[1] Hajj must perform all of its rituals, one of them being the sacrifice at Mina which takes place on the tenth of Dhilhijjah (Eidul-Ad’ha), in order to be able to ‘come out’ of the ihram. It seems your question is about the wajib sacrifice in the Tamattu’ Hajj.

Also, when in the state of ihram, one must observe its haram acts (such as pulling out, cutting or trimming hair and clipping nails which are all haram in ihram), but such acts aren't haram before one enters the state of ihram[2]. Of course, it is mustahabb for one who is going to perform the Tamttu’ Hajj to not cut or trim his hair from a while before (from the beginning of Dhilqa’dah)[3], but as was said, this is only mustahabb and doesn’t necessarily have to be observed and failing to do so won't be problematic for one’s hajj.

Also, it isn't necessary for one to observe all the haram acts of the ihram for the first ten days of Dhilhijjah and as was mentioned, they only need to be observed in the state of ihram, not before nor after it.

In addition, it isn't necessary for each pilgrim to perform the sacrifice himself/herself and can have another do it for him/her and it will be acceptable.[4] As long as the sacrifice hasn’t been made by the proxy, the individual can't shave his head or cut his hair and clip his nails.

The mustahabb acts that have been listed are also correct because acts like fasting, saying takbir, saying Alhamdulillah, doing good towards one’s parents, charity, and visiting family are acts that are mustahabb all the time and everywhere and have more rewards in blessed places and at blessed times, like on the first ten days of Dhilhijjah in Makkah. The great rewards for such acts have been pointed out in numerous hadiths.[5]

Also, repentance from sin is an urgent wajib act (that can't be delayed and must be done as soon as possible) because no one knows when he/she will leave this world, therefore whoever is a sinner must repent as quick as possible.[6]