Whatever paint you use, when you are finished for the day, put clear plastic food wrap under the can lid. This will help seal the paint content from air, make the lid easier to remove next time and reduce rust that forms around the lid from condensation. After sealing with food wrap, store the paint can in your refrigerator. It will increase the paint shelf life. Right now I have three cans in my refrigerator.
What to do with the brushes? Wrap brushes in aluminum foil and store in the freezer. This will allow you to use it the next day, or few days after it thaws. It doesn't work very well with POR because of its chemical nature. That is why I suggest prepping everything first and paint as much as possible on one occassion.
You can paint the tough places on your frame with the body on by using foam brushes. Look in Wal-Mart's paint dept for small flat brushes. The kind with short white bristles, about 1/8 inch or less nap. These are flat, not a roller. For the large areas you can use the dense foam roller available at wally World. They sell roller refills for the same roller handle. Back to the brushes: tie the handle, or just the bristle pad to a coat hanger and you will be able to even get the top of the frame, as I did. This will be a challenge, but do it right and you will get spectacular results. Clean-clean and clean some more before you open the paint can. Most vette owners don't want to show you their underside. I judge an owners committment to the hobby by looking at what is underneith. If you have any future questions, feel free to ask.
BTW...while I was at it I also stripped the fiberglass underside and painted it with PPG epoxy primer with a brush and roller. It came out great and will distinguish your car from everyone elses. You can get this primer in many colors, I used red. Before I did this I molded the wheel wells at all four corners. This is another tough job, but not many Corvettes have this. On the front it helps seal the splash apron from letting water run down the frame rails. Yeah...I even drive it in the rain on the way to and from the track. Molding the back corners makes cleaning them a simple job. Did I say it is a bracket racer, not a show car. Pick your level of finish and roll up your sleeves. I apologize for the long story, but thought you deserved the full detail.