Pooks, it does take some time to get used to the geometry of a road bike. You will notice some neck/shoulder pain your first few rides, but as those muscles strengthen, you'll get used to being in that position. Try to stay lose and keep your shoulders "out of your ears." Keep in mind, too, that men's bikes have wider bars than WSD bikes. Even if you end up getting a men's bike because it otherwise fits, you might consider swapping out the bars to something narrower. The width of your shoulders is a good guide as to how wide you want your bars to be. The beauty of a road bike's drop bars over the flat bars of a hybrid is that you can move your hands around. That helps you remain comfortable for longer.

The Roubaix's headtube is higher, which means that the geometry of the bike isn't as "aggressive" as other race road bikes. Same holds true for Trek's Pilot line. You may find that you like that geometry as it doesn't require as much flexibility and isn't as hard on the low back. Even if you don't buy one of those bikes, however, you can make the geometry of any bike less aggressive by getting a stem with some rise to it. That essentially raises your bars and puts you in a more upright position.

Regarding his comments about steel. He's right that not all steel tubing is created equal. However, I don't think you need to spend an arm and a leg to get a decent steel road bike. Bianchi has some decently priced steel bikes and Gunnar is also pretty reasonable. I'm partial to the Eros Donna an an entry level steel road bike (that's what I have). Give the color a chance!

Regarding core strength. It's an important factor on being strong and comfortable on a bike. Unfortunately, cycling itself will not help you build it. You might consider adding pilates or yoga classes into your exercise routine.

Clipless pedals and shoes. I like using clipless pedals on my road bike, but I agree with Lisa that you don't necessarily need road shoes. You can use SPD pedals if you'd prefer to use MTB shoes (the recessed cleats allow you to walk normally). I further agree that it's a detail you can put aside for the moment.

Since it sounds like you're likely to get--based on your budget--either a steel or an aluminum bike, I will tell you that while AL is often criticized for having a harsh, stiff ride, not all AL is created equal either. The design and tubing used can greatly affect the ride. Remember, too, that you can lessen the feel of stiff bike by upgrading your tires (or if you have some money to burn) the wheels. So, I would definitely keep an open mind about frame material at this point and just test ride as much as you can. You'll likely to find a bike or two that just feels right.

Have fun bike shopping!