1) Both are good choices. About the "dynamic", if you mean to support linear and angular acceleration and brake constraints, that it's not supported in the current brach of stage while it is supported in Gazebo. In any case I work with a modified version of stage which support dynamic constraints. You can take a look: http://rtc-us-ros-pkg.svn.sourceforge.net/viewvc/rtc-us-ros-pkg/trunk/rntl/stage_rep/
2) Using ROS fluently requires some time. However you'll be happy when you learn because you will be able to use tons of software and you will "speak" the same technical language that many developers and researchers.
3) Stage and Gazebo can be controlled using rostopics, rosservices and rosparameters. That means that you can use python to control such simulators.
In other words you don't need to know the C++ APIs of Stage or Gazebo to work with them. You can just use python, topics, services and parameters.
4) If you are a beginer, start with Python. It is enough to try to learn ROS, learning c++ simultaneously may be horrible.
5) As I said, both are good choices.
