I think the amount they could forage it would depend on the season. Less in winter and spring more in summer and fall. We have noticed they are going after the cheat grass seed in our cheep hay that we bought for the goats. One of the things that impressed me the most is they are fully grown in 28 days. Not sure about the 7:1 ratio but we live in a wheat growing country so feed is cheap
Housing: We moved an old shed from a foreclosed on home (Thanks Bank of America and "F" off) it is 12 x 8 we added a exterior fly for them for when we do not wish to let them fly. I am thinking we could have as many as 70 birds in this space.
Poop: Yep they like roofs and leave proof behind to prove it. I have not seen one ever sit in a tree, We are blessed with a stream, water ram, 4k in storage and shallow well for water not to mention 39 inches of rain a year. So rain collection is not our thing. I was looking online for some King Piegons I would like to try them but am not willing to pay the $90 shipping and $50 a bird. The pigeon market is booming we will try to sell some next year if the $ is still working.