1) If you see the verse 2:177 it says that 'if you believe in Prophets'
Now let me ask please how do we believe and follow the Prophets?
The answer is Of course by what they have left for us?
When Quran asked Oh Prophet tell them “ I don’t ask any reward from you for my services except you show love to our Ahlulbayt". Then again question who are Ahlulbayt? And will tell who are they?
For sure Prophet himself. Therefore if it has not mentioned directly about the Aimmah but Prophet he himself is a proof for us. But we have many traditions where it has said about Aimmah and many Verses of Quran also.
2) Yes for sure no one in Islamic History deserves other that Imam Ali (a.s) for this ayah
إِنَّمَا وَلِيُّكُمُ اللَّهُ وَرَسُولُهُ وَالَّذِينَ آمَنُوا الَّذِينَ يُقِيمُونَ الصَّلَاةَ وَيُؤْتُونَ الزَّكَاةَ وَهُمْ رَاكِعُونَ
Only Allah is your Vali and His Apostle and those who believe, those who keep up prayers and pay the poor-rate while they bow.(5:55)