Need advice before starting my membership site project

I recently got idea :flame: about creating IM forum in my country since there isn't any.
I know that I need domain, hosting, forum template, email (+aweber after some time).
I want to make it as membership site : registering and reading for free, posting and advertising for monthly fee.
Since I don't have any experience with membership site I got few questions :
What to I need to make it like membership site ? Some script ?
How can I get detailed overview about my paying forum users ? How can I allow them certain features right after paying ?
How can I make different levels of fees ? ( 5/month for posting, 50/month for posting and advertising )
What else should I know about membership site's ?
P.S What forum template would you recommend ? I need features like ranking, private messages, profile customizing and so on...
and also : What plugins should I get ? (wordpress)

Thanks for every answer
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