We have done greens. They get lettuce, mustard, collard, turnip. Really anything growing in my garden that I decide to throw in. They are not laying yet but I expect them to at any time. They are about 18 wks. My boys just get chick starter and the girls all get layer pellets and scratch feed. I have been thinking about changing.Congrats on your new ducks!! The tail will start curling closer to 4-5 months, but you will be able to tell male from female sooner simply by their voice (loud quacking - female, raspy/whispery quack - male).
On the snacks, no bread, onions, or potatoes - or at least limit them. Stick to lots of greens and/or bugs - good healthy lettuces (limit spinach) like arugula, romaine, kale, dandelion greens, etc. Frozen, thawed peas are a super favorite! You can also get mealworms, earthworms, etc. Minnows in the pool are always fun!
IMHO - never give layer feed. It's just not a good healthy feed - too much calcium if you have males. It's hard on their organs to digest that much calcium and in turn can shorten their life span. I prefer to give all my flocks (ducks/chickens, all ages and genders) a grower/flock raiser forever. Then, I just provide calcium on the side and they can all get it when they need it - they know better than I. If you do decide to use layer anyway, don't use it until they start laying - it's very bad for young birds - actually depletes the nutrients they need for growth.
X2 on kodster's reply - as long as they have shade and water, they will be fine.
Are they laying yet? If so, you can start providing oyster shell on the side - giving them eggshells is fine too... won't hurt them at all.
As for the leg, it is hard to say but I would maybe add some niacin to their water for a little while and give some extra greens that are high in B vitamins - might make a difference with the healing process.