Advise needed for multiple private areas structure and installation!

I need to build a website with a public area (just pages) and a Private Area.

Now, there will be different access to different sections/areas depending of the Roles.

The sections/areas are actually countries, 18 in total:
Country 1, Country 2, Country 3, …

I will therefore have different Subscribers Roles: Subscriber Country 1, Subscriber Country 2, Subscriber Country 3, …

I will also need Authors who can write (“Events” as custom post type), and of course read on their section: Author Country 1, Author Country 2, Author Country 3, …

Than I will have an Editor Role, who can access all the information, publish everywhere and all. And than one Administrator (me) to be able to modify the backend (add plugins and stuff that the client/Editor, shouldn’t be able to do).

I am wondering if I should go for a MULTISITE installation, as I don’t have experience with that kind of WordPress installation (did use BuddyPress on one site, thought).

For the moment I am building it all on a regular WordPress installation, but I start to run into complicated issues, as with the Authors and Subscribers capabilities.

For example, the Private Area will be structured so:

Private Area (login page: when a user is logged, depending of the role, will be redirect to the appropriate Section/Area):

Region 1 >
Country 1, Country 2, Country 3

Region 2 >
Country 4, Country 5, Country 6

Region 3 >
Country 7, Country 8, Country 9

Region 4 >
Country 10, Country 11, Country 12

Region 5 >
Country 13, Country 14, Country 15

Region 6 >
Country 16, Country 17, Country 18

– –
Every “Country” is a page displaying:

Ateliers:
– Future events
– Past events

Workgroups:
– Future events
– Past events

Fora:
– Future events
– Past events

Other pages (static)
– –

I created an “Event” post type, with taxonomies: Event Type (Ateliers, Workgroups, Fora), and Event Country (Country 1, Country 2, …).

So, should I go ahead and have a very complex page structure with all this subpages under the page “Private Area”, or should I go with a Multisite installation?

Also, one problem I am encountering is that the Editor and Administrator should be able
to view the different Private Areas, but for the moment I display the “Events” according to the logged in Role’s Capabilities, but the Editor and Administrator have ALL the capabilities, so how to enter an area and not having all the “Events” from the other areas showing up (using a condition checking if the page displaying the events is a child of a country section, for the moment).

Any advise about it all?

Thanks in advance…