Shared access to multisite network

Can you please let me know if S2Member works in my specific situation as well?
I have a subdirectory network multisite site. The idea is for clients to login (following registration and password) through the portal on my homepage, and then from there on they’d have access to all the subdirectory sites that i allow them to have access to. So no further logins. It wouldn’t work for me to have a separate install on each subdirectory site, because I don’t want my clients to constantly login if they browse my site(s).
The idea is that the plugin allows password protected access on the main site that provide access to members-only content on site(s), pages, posts, etc throughout the entire multisite network. So, one access point for the entire network, with access based on (custom) categories (company names mainly). Login credentials should be shared across the entire network.
Clients could have private pages/site, but I would generate the content. So, all users who are employees of client company A would have access to dedicated company A content (rate lists, dedicated products, etc) and general access available to all logged in users.
Lastly, I am not selling subscriptions etc, this is strictly a free info/training/brochure site for our clients. Registration is therefore subject to my permission. Is this possible, that registrations are “on hold” until i accept them?