Hi Paolo,
As for the best approach for your problem, our Professional Services team would be able to better assist you. Let me know if you would like me to get you in touch with them.
As for your last question, yes, you can have an n-tier and a 2-tier EntityManager. You can always set IdeaBladeConfig.Instance.ObjectServer.ClientSettings.IsDistributed dynamically.
Note that you will need to have connectionString set in the client's app.config (or resolve it dynamically)
Regards,
Silvio.