I dont think chickens going completely "grain free" is really an option. Now a number of people will use a combo of sprouted grains as fodder, grow meal worms and other worms. Plant chicken forage etc to give them more of a natural diet. The real issue is scale. You can feed a small flock on free range kitchen scraps with some supplemented fodder etc some mix their own feed but that is usually expensive unless you buy in large qty. Feeding the flock is really a matter of scale. Most free range flocks are supplemented during winter months when forage is light. If you want hands on experience start with just a couple of pullets in a small coop, it can be done cheaply, to get your feet wet. If you find you dont enjoy them it wont be hard to rehome and your infrastructure cost wont be much (find a large used dog crate to serve as the night box. The rest of the run and enclosure will depend on your predator situation but for most suburban back yards the dog crate will suffice. As far as feeding you can get an idea from two how things might scale up.I want to get hands-on experience raising chickens before I even make a decision to do this in my backyard. I may actually have to sell a home and buy a new one to get the land to do this properly, so it is a huge decision.
I am going to research exactly as you describe above, but only *after* I get hands-on experience first. I don't want to make a major time and life commitment to something and then discover at the end I hate it.
My real first preference would be to find a chicken farmer who is willing to experiment and try to feed a grain-free diet. So far I have not had luck with that.