I have been raw feeding for about 7 months, so by no means am I an expert. However, I will answer your questions as much as possible.
Can you switch cold turkey?
-Depends on the dog. Some dogs, yes, some dogs no. Our puppy switched, one day we started giving him commerical, and he took to it, then didn't want kibble any longer, so we switched him. We still offered kibble to him, but he wouldn't take him, so he switched himself, and he was fine. If your dog is having diarrhea, then switch slower, the point of switching is to make as less stressful for the dog as possible.
Should you worry about non-organic chicken?
-This is a personal preference, we don't' feed all organic, but we check sodium levels on all chicken before purchase. I think that is the important part, making sure your sodium levels are in the good range.
Can you use only one protein source?
-The common answer to this is no, it is recommended you use 4 different protein sources. We use chicken, turkey, pork, beef, and sometimes salmon, goat, lamb, and rabbit, when it is available. Your dog will get different amounts of nutrients from different types of meat, so variety is key. Leaner vs fattier meats are going to have different health impacts. Also, some believe that feeding 1 protein source can increase risk of food allergies later in life.
I hope this answers your questions! I am by no means an expert, and hopefully some more experienced people get on here. Maybe Moms will see this.