opengl drawing project and selection

I’m implementing a simple project for bidimensional shapes’s drawing using opengl.
I already implemented a little engine for manage vbo buffers ,camera and shaders.
The 3d scene is incapsulated in a qtGLWidget of qt 4.8.
Now i would create the drawing of a point, a line ,a polyline and some circles,
1)what are the better rapresentation methods of these entities?a parametrics rapresentation?
2)i would implement a mouse 3d picking and i saw a demo for this, but was used a bounding box system for this(with a bounding sphere), there aren’t more accurate system? or is sufficent change the bounding sphere in an axis oriented bounding box?
3)how i can implement a box selector? with the drawing of a rectangle from the start point clicked , to the current mouse position,without Flipping with a shader?

There is a good demo or tutorial

I use opengl 3.2


If you are using shaders, here are few tuts which can help you.

But before that this is good for beginners

Recently new website has been launched for opengl 3.3 tutorails…

Good luck