developing social ecosystem to empower freelance journalists

[Satya]

Hi All ,

I'm a joomla developer and now playing role as a architech. we are
developing social ecosystem to empower freelance journalists. In
ecosystem we have 4 Site. all of 4 site can access bassed on
permission and subscription system. :o

I'm wondering what is the bast architecture. Now I've two option:
1. All of site feature implement in one joomla site.
Challenge:
- How to manage different domain for all of site.
- Site performance issue may be come if all of the feature include in
one site.
2. Use four joomla setup and implement site feature in site.
Challenge:
- How to Implement centralized login and registration system.
- How to manage user session on all of the site and provide correct
permission.
- How to display one site data on other site[If user have permission
then any where he can access all the site feature in one place]

My thought implement 1 and accept 2 challenge :)
What is the best way to implement Please explain me. ??? :-\