Istikhara (2):

Q1: a) Is there any proof of Istihara in the Sharia?
b) Is everybody allowed to do Isithara for himself?
c) What are the rules of Istihara and is it allowed to repeat an Isithara for the same occasion?

A: There were narrations that explained the idea of Istikhara which is seeking goodness from almighty Allah when deciding to do a thing. This kind of Istikhara is common in the narrations. Books of narrations and supplications have explained certain ways to do the Istikhara.
Yes, it has been reported that Istikhara becomes the way to choose the right position in cases of hesitance and uncertainty in finding out the best choice for a person. These narrations did not specify the person that must do the Istikhara, so anyone is allowed to do it for him/herself or to others.
There are no specific conditions to the Istikhara but it is suppose to be done when the right choice is lost and there is no meaning to repeat it after it has been done.

Q2: Since we cannot directly follow Imam of time and it is obligatory to follow the most knowledgeable jurist (mujtahid), I want to follow a mujtahid who is most learned (al-a'lam) jurist of his time and the most capable in deriving the religious laws from the appropriate sources. I’m unable to find ahlul khibra (those who are sufficiently knowledgeable in Islamic jurisprudence) to refer them In order to determine who is the most learned mujtahid. However I have found multiple jurists (mujtahid) those jurists have all the necessary qualification to be emulated. I want to be certain that a particular person is the most learned (al-a'lam) jurist of his time.
Is it OK to do istikhara for such situation and will my taqleed be ok?

A: It is not permissible to depend of Isrikhara to choose the right Mujtahid to follow. If they were equal in knowledge or you were not able to determine the most knowledgeable and one could not act in such a precaution that guarantees that the religious obligations are fulfilled, one must choose the most god fearing amongst the most knowledgeable Mujtahids. If this was not possible, one of them can be chosen to be followed.