So, potentially a stupid question but, if you have a butt ton of land (say 2-3 acres, my grand master plan is for 15-25) for them to roam on with a compost heap, do you need to feed them more? Or, is more on top optional for making them as fat as possible as fast as possible?
That's not a stupid question at all, it's a fascinating and useful one, but I think that's hard to say. There are a lot of variables, like the size of your compost heap, how it's managed (lots of insects, or too hot for them?), the quality and type of forage available (bug-rich leaf litter, fallen fruit?), your weather patterns and climate (chickens can't forage adequately on frozen ground or snow), as well as the type and breed of chickens (games or landraces usually forage better, and smaller chickens need to eat less). Also what you're expecting to get out of the flock--it's easy enough for chickens to get enough nourishment to survive, but if you also want a lot of eggs, or want them to reproduce efficiently, that requires substantially higher quality feed (whether foraged or provided). This is why wild chickens scavenging the woods don't lay all the time, they lay a clutch when the abundance of food allows them to produce one.
Setting up a forage-based system is a great way (if not, in fact, the very BEST WAY!) to keep a flock, and chickens can convert the diverse feed sources available in the landscape into nutritionally perfect eggs and meat, and be supremely happy doing so. But you can't ever get something for nothing, and the results are only as good as the environment you provide, and your choice of breed. I think most people in reality will end up feeding something, but it could just be something like cheap grain, or stale bread, or scraps, if the forage is good enough. Also, feeding them something, even just some scraps or treats, provides an incentive for them to stick around, and can keep them tamer, in case you ever need to handle them.
Also, I don't think that 2-3 acres is a "butt ton" of land for anything but a rather small flock of chickens if you're envisioning an exclusively, or nearly exclusively, foraging based system, but like I said, it depends on what you've got there (a giant compost heap could definitely help--also things like orchards or berry patches, or manure-filled pastures will up the carrying capacity). Where I live the wild/feral chickens (which are the ultimate foraging breed) forage in small flocks of usually less than half a dozen over many acres, adjusting their habits seasonally based on what fruits are in season as so forth. You only find large numbers of them congregating in one area where some process, usually human-created, has provided enough resources to support them, like campgrounds, garbage dumps, neglected orchards, etc.
