Crockpot recipes generally suggest browning the meat first in a pan (browning or searing, not necessarily cooking all the way through) because of the flavor this step imparts to your dish. The high heat also has the added benefit of killing off any surface bacteria that may have formed on your raw meat (the crockpot doesn't get hot enough to kill all food-born bacteria).
Just to be safe, go ahead and brown that chicken in a pan over med-high heat before tossing it into the crockpot with your broth and veggies. I'd add the noodles later in the process or even cook them separately and add them last, since cooking them over low heat for a long period of time will likely result in a gooey mess.
We cook in our crockpot at least once a week, and have discovered that most recipes require a cooking step at the beginning and again at the end. (Since water doesn't cook out of the pot like it does in a pan, we often have to reduce our stocks and sauces on the stove top once the crockpot has finished cooking). Basically the only benefit of the crock vs. the stove is that you don't have to tend to it during the cooking process. Which is still awesome!
Happy soupmaking!