Yes, in fact, bacteria livein the clouds on Earth, and this is even a richer atmosphere. But that isn't necessary, people could live there NOW, as it is NOW. 45-60km is a sweet spot in the atmosphere, EXACTLY LIKE EARTH, and it won't take energy to float around there, and you would have everything you need for life.

Plants would grow 3-4x faster in a greenhouse with abundant CO2 and sun, which would supply you with endless oxygen. The atmosphere has almost everything a person and greenhouse would need to survive. I mean, you may need some trace minerals like Magnesium & Iodine, but the most necessary and common things are available. Oxygen, Nitrogen, Sulfur, Hydrogen/Helium, Water (I guess), normal gravity & pressure, free energy, etc. And once enough colonies are established, I am sure they will figure out a way to mine things and make some cool cave habitats.