I would run a 5w20. There are a batch of 5w20 oils that are on the dexos1 approved list. Not really sure why anyone would be hard core about using a 0w20 except in some pretty cold conditions. Especially when 5w20 generally has a lower NOACK rating than a similar brand 0w20, and that could possibly be of benefit to the VVT and AFM stuff going on in the 6.2L.
While it is true that OEM's are recommending the 0w20 a lot, it also needs to be taken in perspective that it is the grade that they do their CAFE and EPA certs on and from what I have heard, they have to recommend the same grade of oil that they used for the cert testing.
Onto the catch can thing. They are installed on the PCV line between the port on the valve cover and the intake manifold. They separate out oil and gunk that gets thru the port before it can get into the intake. Those oily vapors can build up on intake valves and increase chances of some serious build up on them. And since the 6.2L is a direct injection, there is no fuel "washing" the buildup off the intake valves. Using a catch can is a prudent measure I would take. I use them on my personal vehicles. You can buy a few good brands, and many mediocre to lousy brands. The better ones tend to be the Elite, the RX, the Conceptual Polymer, and the Mishimoto. I use the Conceptual Polymer HE version on my Silverado and an Elite on my Cadillac.
