Unmedicated chick starter is ok to use to increase the protein content of a homemixed feed - the reason the teenage chickens need less protein than chicks is to prevent the reproductive system from developing too quickly leading to prolapses and things of that sort from what I have read on BYC...
Flaxseed meal goes rancid VERY quickly so you would want to use that up quickly. That's why you see the flaxseed oil in the refrigerator at the health food stores.
Have you looked into peas? You cannot rely on them wholly as they are low in methionine (sunflower seeds are higher in it):
A...
If you like, you can see my BYC page for what I feed. One way to do it is by adding seeds, ROASTED soybean meal, unsalted peanuts, scrambled eggs, fish meal (be careful with that one...make sure you know that it is for poultry feed and not gardening or rancid).
Do not feed gardening products...