on the games I've worked on so far, if the engine was not capable of rendering double sided faces, I had to literally duplicate the model and reverse the normals. Then it'd be psuedo double sided.

As for selecting your model, you can untoggle joints in the selection masks if you just want to select the mesh. If you're trying to move your rigged character as a whole, you don't need to select the mesh, since it's bound to the skeleton. Select your root joint and any IK handles you have (or their groups if you're using a method similar to how I rig things) and then you should be able to move it all together.