Regarding the guidance, the view towards imamsImams is similar to the view towards the prophetProphet. Shia do not believe that imamsImams can guide independently from God, the guidance is only from God. The views towards imamsImams being infallible is similar to views towards the prophetProphet being infallible. The arguments regarding why they are infallible are more or less similar to why Sunni believe that the prophetProphet is infallible.
Many Shia believe in a stronger version of infallibility than Sunni Muslims about prophets and hold the stronger form of infallibility towards imams. The main verse used for this infallibility is verse 33:33 in addition to hadith regarding who are the ahl al-bayt. There are also some philosophical arguments a number of other hadith attributed to imamsImams themselves regarding infallibility.