1. Why would planets be required at all, if the universe was uniformly warm?
2. My microwave oven also heats things to the melting point of water, but I would not call it hospitable to life.
1. True. Organic compounds have been found in Nebula. We don't know if gravity and "ground" are necessary to turn it into life.
2. Although the study uses the traditional term for the background radiation "Cosmic Microwave Background", technically, it likely wasn't microwaves at that time, but closer to the visible light spectrum (maybe even beyond that). We only see the background radiation as microwaves now because the EM waves have stretched out due to expansion of the Universe.
2. You're right, I feel silly for not realizing that.