DO NOT offer "Flock Block" - its basically Scratch, only without the ability to control how much treat they eat. Really mess up a complete diet. You can offer veggie scraps, thin layers of cut grasses, and other things to encourage scratching behaviors. Or you can simply throw a bit of food - they think that's a treat too. or make oatmeal out of it - they think that's a treat, too.
Flock Raiser is Complete. It may be a bit low on niacin for some breeds of hatchling ducks, but for chickens, its got you covered.
Yes, crumble any age.