You could add veggies and fruits, but it'll just be filler. Dogs don't need that stuff, and won't get any nutritional benefit unless if it's pureed or pulped to mimic stomach contents.

I would hand it to them whole, you might be surprised. Unless if you want to be chopping it up for them each time, you are setting yourself up for finicky dogs by doing that if they refuse it whole. Fish is one of those foods that my dogs crave. Mandy goes absolutely nuts over fish, probably because it's so much stinkier than other meats.

Chicken breasts are fine, bone-in or boneless. Chicken legs are kind of small (it's easier for them to choke on smaller pieces), I'd get chicken quarters. Quarters are usually cheaper too, I just got 20 lbs for $.49/lb. Some dogs are really good with eating legs though, it all depends on what type of eater your dogs are. Nova and Luka will practically swallow a leg whole, so I usually feed them quarters or whole chickens.