Regarding inflation of prices - if feeding everyone leads to inflation of prices then in principle we can't feed everyone. That says more about resources than it does BI, if I understand you correctly. I think if we were to do this, we would need the capital and infrastructure to handle the increased demand, maybe outside the traditional economic system so that prices didn't increase so much.
Going from a system where everyone needs to generate $20k of economic value "to eat" (yes, oversimplification of benefits, but bear with me) to one in which no one needs to generate economic value may have some macro scale inflation issues.
Those are the issues a study of UBI needs to cover.
