Best data binding strategy for REST web service using Axis2

[Public Network Services]

Hi...

I want to build a REST web service using Axis2 1.6.1, with the following
basic *client characteristics*:

   - Remote login/logout
   - Session management
   - Continuous data transmission

Each client will be continuously posting serialized POJOs to the service
over HTTP or HTTPS. Each POJO will contain a small amount of data (a few
KB).

Mapped JSON will most probably be used for the serialization part.

Given the above:

   - Does it make sense from a performance/efficiency perspective to use
   JSON (as opposed to raw XML)?
   - Is AXIOM the only possible/advisable approach for data binding
   (especially for JSON)?
   - Is there any way of enforcing a maximum data size (length) at the
   service side (e.g., for security purposes)?

Thanks!