My aim is to generate massive traffic and use automated membership service (content/levels/payments options).
s2Member can handle this. It will take some work, and the
specific passwords to certain posts
will not be valid through the s2Member plugin. Unless I'm wrong the password you have set up for the posts should still work separately from s2Member, and if you want to protect them using the plugin, you will have to take the passwords off and instead use the plugin's protection.
As in, if you protect the post with s2Member, it will not automatically remove the password.
Is that what you are talking about?