The first couple of requests could probably be done using vbulletin (they already have paypal integration for subscriptions, you would just need to learn how to manage users and subscriptions and is a forum so that's nice), or you could try a few of the other CMS's. Most have user management systems built in, and have mods that can extend the functionality. it'll get kinda hairy, but at least it'll be a system you can grow with. Start with systems like Joomla, Drupal, or Wordpress, and check for subscription mods or something.
As for the plan text forum type functionality, vb has a light-weight version, and the other CMS systems probably have something simliar. once again, the functionality will probably be achieved through a mod for the cms.
have you worked with any of the CMS out there?