Question and answer forum website like quora

I want to create a question and answer forum website where a user can ask the question and the experts or admin can give the solution. There are two types of questions, one is free and other one is premium. If a user wants to access the premium question answers they have to pay a small amount of fee in form of daily, weekly, monthly plans. Upon purchasing a plan, user can access the premium materials for a given time frame like 24 hours or a week time or a month. Users are allowed to post the questions and comments to the answers. Answers can only be given by the experts or the admin. Once a user post a question it should go to admin for approval and upon approval it will show in the question forum list. The experts will answer the question and again it will go for approval. If admin post any answer then directly it will show answer to that question.