Thanks to the people that replied, but I think I was not clear enough on my needs.

I try to explain better:

1. when you login you should be redirect to profile/edit page where you must fill the compulsory fields (at least Name, Surname, Email and Location). The location field should have the possibility to pin the address on a google map or at least use its autofill feature in order to grab a real address.
    
2. When you login and complete your profile, there should be a verification step: e.g. if at least three people verify me I will have full access to the site, with the limits of point 4 below; or the admin can do it.
    
3. I would like that everything is added to the site by the geolocated user has his same location: if he posts on a blog, on the wire, on the market, etc. every activity he made is anchored to his location. (I believe this approach is more consistent and straightforward than geolocalize each post)
    
4. the site must be a walled-garden one, where the limit of the things a user can see or interact with should be around a given circle around him (i.e. 1km). So in order to use the site you must login, but everything you see is around 1km from you: for example, if I click on Activity, all I see is the activity around me, the same for the Market, Blog, Wire and all the other features elgg supports.

I hope it is a bit clearer now. I am here for any comments or questions.

The Coldtrick's group_tools plugins allows for suggested groups upon registration and also (AFAIK) automatic group joining.

hmm, maybe the "roles" plugin (together with the profile_manager plugin?) allows for additional permission types that also effect what menu items can be seen? Never tried it though.

There is one solution that might closely resemble what you are trying to achieve. Create invisible groups and let group owners or members invite new users using group tools. It will send out a link and when the user registers with this link, he/she will be joining that group. Joining other groups is impossible since all groups are invisible.