Some modifications to meet my need

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I wish to create an advice site using q2a where users can ask for advice even for secret matters and others users can answer to their troubles. By implication,

• I need a category based system

• I need users to follow each other like twitter profile

• I need users to follow other users' questions, answers etc (Get notifications for this question)

• I need users to choose whether none follower can send message or not

• I need users to choose to be able to chose whether to post as anonymous or to post with their profile showing

• And I want users to be promoted to consultants based on their performance in giving answers to questions. So users can be promoted to consultant for a category or multiple category.

What will it cost to get these done and how long?