does coverting my model into mesh will make it lighter in size and easier to navigate ??
… and if so does my material stays embeded in it ?
In large scenes with lots of objects, using meshes can speed up the display, yes.
When you use
ExtractRenderMesh, the material of the NURBS object will also apply to the mesh object.
When you have several objects that share the same material, you can join the meshes into a single mesh to further speed up the display.