Just a warning, I am not a professional and my knowledge are based on research, not real life experience :( and I hope you understand. Hope this helps!!
1. I would consider this as a rather great feed, as long as you calculated the protein percentages correctly. Did you? If not, here is a website that may be helpful:
http://www.lionsgrip.com/protein.html. Go to the section called Kim's Rectangle for calculating the protein in a MIXTURE OF GRAINS.
My recipe is less elaborate as yours and not gluten free, so I am now considering to use your recipe instead!
Chick Starter Feed: GRIND
Wheat 2 parts
Whole Corn 2 parts
Milo 2 parts
Peas dried 1/2 parts
Soybeans dried & roasted 4 parts
Protein Percentage = 20% (Note: both percentages are calculated using the method from the link above)
Basic Chicken Laying Feed:
Wheat 3 parts
Whole Corn 3 parts
Milo 3 parts
Soybeans dried & roasted 2 parts
Protein Percentage = 17%
Chicken Feed Additions:
Egg Shells for calcium
2. Yes, you can use this for developer, or otherwise known as grower, feed. The only difference between layer and grower feed is for grower feed, skip the excess calcium. They will need them only when they start laying eggs. Too much calcium can damage their liver. Also, there are many other supplies of calcium that is available - alfalfa hay (1 flake for 8 to 10 chickens once a week), crushed eggs shells (don't use if you don't prefer), and even something called limestone, which I don't know much about.
3. My only two recommendations about your recipe is, do not feed mealworms to your chickens so often (maybe once a week as a treat), and make sure your chickens have grit available to them. Small treats can raise a chicken’s protein intake, especially when young or during laying season, isn’t a problem. Since chickens who are allowed to range naturally scratch for bugs and worms, supplementing with mealworms is in line with their natural instincts. Grit (otherwise known as small particles of stone or pebbles) is very important, and helps chickens digest some tough food.
4. Unfortunately, I am not familiar with any gluten free feed because I myself is gluten tolerant. I hope someone else can help you with this soon, but I don't understand why you need to find a brand of feed if you already have a homemade recipe to go.
I hope you have success with your new recipe and have your chickens live a long, productive life!
By the way, your profile picture is adorable!!