We are considering the use of Multi Site to manage numerous domains with one Joomla installation. All sites are primarily JomSocial communities. Each community might have dozens to hundreds to thousands of members.

Our goal is to minimize the maintenance workload. Multiple individual domains will run on common Joomla core code and common extensions. All domains run the same version of Joomla, JomSocial and so on. Any update of Joomla and any extensions must apply to all domains.

Templates
Several templates might be in use. Typically there would be one default template per domain. Some domains might share a template but would need custom CSS files. For example, three domains might use the Protostar template but there must be a way to include a domain-a-override.css file for domain A while domain B includes its own domain-b-override.css file.

Menus
It must be possible to use different menus and menu modules in each domain.

Administrative Access
The Joomla administrative users (back-end) will be common to all domains. The JomSocial non-privileged community members, on the other hand, will be exclusive to one and only one domain.

There might be privileged, front-end only members that have access and common logins for a selectable group of domains. For example, manager A needs a single user name and password to log into the front-end of domains A and B for the purpose of administering that manager's domains.

Mobile Apps
Each domain will have different iOS and Android apps associated with it.

Backups
An Akeeba backup must include all domains.

Is this scenario possible and recommended using Multi Site?

1) Template.
If you want to change the CSS of a template per site then you have to install a specific /templates directory per site.
Because the CSS are saved in a directory on the disk, you need to have this directory specific per site. Otherwise, it will be shared.
To have a specific /templates directory, you have to create a new JMS Template rule in which you specific that you want to do a copy OR keep "special copy" and specific the template directory = {deploy_dir}/templates.
See partial template sharing - page 22 - PPT www.jms2win.com/en/documentation/doc_details/27

2) Menus
By default the content of each slave site is specific as long as you use a specific DB or at least table prefix.
Only the extension for which you specifically request the sharing of the content will be shared between the website.
As the menu are defined in the DBs then the menu are specific per site as usual with a specific instance of joomla.

3) Administrative access
By default, the users are specific per site.
If you want to share the user, this is possible and must be defined in a JMS Template rule.
JMS provide some default rule called "shareMasterxxxxx".
See also video 16 that explain the sharing.
www.jms2win.com/en/tutorial#jms12x-16

If you want to have different ACL per website, you will also have to consider the usage of the "Partial User Sharing" extension.
See www.jms2win.com/en/joomla-multisite?page...63&category_id=1

Remark: JomSocial does not allow partial sharing.
If you need a partial sharing, use "EasySocial" that includes partial sharing facilties.
This will allows you creating communities per site.


4) Mobile Apps
Yes this is possible.
JMS Medium or higher also give you the possiblity to create specific website depending on the browser features. So you can also create specific website dedicated to the mobiles.

5) Backups
Akeeba backup only backup 1 sites.
If you want a backup of all sites, you can use our "Weekly backup shell script" that is able to perform the backup of all sites and DBs in one shot.
www.jms2win.com/en/component/docman/doc_...ackup-script-all-dbs