I was wandering if it would be easier working with a modeling agency or without one?  If you do work for them do you get paid doing it?

In many jurisdictions it's illegal for a modeling / talent agency to be directly associated with a photo studio (or similar companies such as printers, schools, etc).   This is to insure that the agency gets paid for the work they are supposed to do (finding employment for the talent) instead of making money from selling the talent items and services they may or may not need.

In those instances an agency may be allowed to refer the talent to photographers, but can't demand they go to a particular photographer.

That's the way it works in a perfect world, but the real world consists of 'kickbacks', which are often illegal but difficult to prove.  Many photographers give such 'gifts' to an agent for recommending them to a model.