I don't know Chicago's climate, but here in So Cal it's dry and not too much humidity, so I was able to leave large portions of metal without any coating for a long time without any rust. Plus, the car was in my garage with a cover. I would definitely put a coating on bare metal if I were you.

If you remove the skim coat/filler process, the order in which we painted our cars is not much different. Notice he used a sealer. You should check your materials to see if this is recommended. Sometimes it is, sometimes it's not necessary.

My garage isn't setup to spray, but I managed my painters work closely and he worked with a PPG rep using waterbase paint(yes, I live among a bunch of tree huggers here in California).

Sorry, no experience with SEM's product you mentioned.