Multisite Network - Paid Posts

I am looking for advice on how to create a Multisite network with the following features:

1) One login to access all subsites (?)
2) Front-end guest post form on each subsite
3) Restrict ability to add posts - paid form only (?)
4) Member account page to view/edit paid posts (?)
- This could be on the main site, or on each subsite

Plugins: So far, I am using Domain Mapping, Formidable Pro (forms), and Tips & Tricks eStore (payment) and WP Affiliate for tracking affiliates across the network. I could use AAM to restrict posting, but I would like some other ideas on how to do that.

I don't know how to create the universal login across the network. Can this be done with Domain Mapping? I also don't know how to create the member account page that gives users access to their paid posts. This might be a feature in Formidable Pro. I am new to this plugin and still trying to understand it. If it's available, then I would use Login Redirect and create a page that lists paid posts 'owned' by the users. Any idea if that's a possibility?

Any help would be much appreciated.