Step 10: Modeling the arms
For the arms you can use box modeling instead of line modeling, which means that you start with 2 extruded tubes coming out of the armholes of the shirt, ending in your pockets if you don't show your hands (Don't forget to merge the points to the trousers. If they refuse to merge, try to join the solids or make the value bigger).
Then use the Cut-Faces-tool (Shift C) to divide the arm into 6 - 8 parts and form the elbow and the beginning of the hand. In the top third of both arm parts it gets a bit thicker, that is really important for them. Again exaggerate a bit with the proportions.
Texturing is very easy if you don't show your hands. Simply use a high resolution skin texture and make it a bit lighter in the middle. You need 2 textures, like in step 8. What differs the front from the back texture is only the small but effective inner elbow valley, as shown in the picture. It should be easy to draw with the lighten/darken-brush.
When you are done with the arms, delete the rest except the size-rectangle and export them as a 3ds-file.