I think he is my best friend.

Question 1: him is the object, and my best friend is the complement, because he is my best friend and has the relationship of the main system table.

I read fluently. Do you think it's easy to add mine as before? In fact, this as can be omitted.

Another example: I asked him to be our leader (we chose him to be our leader), which is also a sentence pattern of subject-predicate and object-complement.

Question 2: You can use the object clause as the object, and the analysis is correct. It is synonymous with the first question.