Unless you are moving your saddle back over a couple cm, you probably won't need a new stem. Even if you do move it back that far, you may find that you still feel comfortable with the reach just because you aren't leaning so hard on the bars. Before you buy a new stem, you could try adjusting the angle of your current stem to bring the bars up and a little closer to you. If that makes them too high, remove some spacers and then angle the stem up.

You also asked about what your shoulder/arm profile should look like on a road bike. Here are some examples of my positioning (note that I am not claiming that I have perfect positioning--in fact, my positioning is a bit abnormal in that when I race I have a lot of elbow bend and my bars are a bit high--not aggressive saddle to bar drop--but it's still what's comfortable for me).

Relaxed in the drops


Crit racing in the drops (I'm sitting pretty far forward, though my saddle hasn't moved)


Relaxed, on the hoods, compared to a friend with more aggressive positioning



TT effort, climbing, on the hoods