Hermes

You will be more aero, use your gluts more (more power) and shift weight off your sit bones to your hands. However, there is a balance to be maintained and gradual changes are better than large changes to allow your body time to adapt.

It is easy but I would take it to Adams. I believe the Roubaix has carbon parts. It is easy to over / under tighten the stem and to flip the stem or remove spacers, you will have to retighten the headset. I find there is an art form to getting all that right for carbon parts. I let my mechanic do it or I do it to a snug fit and have them check it. If it is all aluminum, then you can do it yourself.