A decent home mix should have a wide range of grains, some low-toxin legumes (e.g. cooked soy, peas, alfalfa) in careful quantities, oilseeds like sunflower, b-vitamin supplements like yeast or soured milk (the latter also good for methionine), and fresh greens. It's not easy to get right, especially at first, as there are big temptations to go for cheap rather than better ingredients. Sprouted grains are usually better than whole (vitamins more available).
I've done a fair bit of experimenting with home mixes, and have also made some big mistakes (like using sweet lupins instead of soy). I think if I'd gone for whole cooked soybeans I would have been just fine, as I added kefir (soured milk) for methionine, and growth was pretty good overall. My birds are penned so every aspect of the home mix is crucial; with free range it's a lot easier.
Overall I'd say do it, but don't be tempted to ignore advice on inclusion levels for things like alfalfa, sunflower, peas etc, and do keep an eye on the birds (and particularly on their laying, which is usually the first thing to alter when there's a problem).
cheers, and good luck
Erica