1) YES you can share the users between the master and a slave site or
between slave site (not necessary with the master).
This is shown in the tutorial video 16.
www.jms2win.com/tutorial#jms12x-16
You can also benefit of the single sign-in when you share the users between
websites on the same domain (either different subdomain or subdirectories).
If the users are shared between different domains, they have to relogin with
the same user and password.
2) When you has Single Sign-In, the session is unique.
In fact the session ID is the same when working on the same domain (either
subdomain or subdirectory).
3) The remember me works with the cookies.
So if you are on different domain, you don't share the cookie.
4) The concept of JMS Multisites is the sharing and NOT the syncrhonisation.
The difference between sharing and synchronisation is that in the case of
syncrhonisation, you suppose that you copy the data that you need later
syncrhonise.
With the sharing, there is no duplicated data. The data is present only
once. So no need to syncrhonize something that is unique.
You can NOT decide which MySQL table can be shared.
5) Not applicable - No syncrhonisation but sharing.
See the tutorial video 0.a that present the concept.
www.jms2win.com/tutorial#jms12x-0a
6) Not applicable - No syncrhonisation but sharing.
7) Each website can have their own extension.
The only constrain is that the extension must be previously installed on the
master.
The master should be considered as a repository or a library where all the
extensions are installed.
8) YES. See the list of extensions currently defined in JMS Multisite tool
and also the one that can be shared.
www.jms2win.com/component/content/article/135
9) YES JomFish is defined in JMS Multisites.
I also suggest that you have a look in the tutorial video 0.d that present a
demo overview.
www.jms2win.com/tutorial#jms12x-0d