1. You can do this on-line or at check-in. TSA will not let you go through security without the phrase on your BP.
2. No you cannot sit in an exit row. Yes you can sit in the premium seats. If your travel is on a RJ please keep in my you must sit on the CD side. If it's on the ERJ it must be an even row, but not the first or the last, and on the right hand side.
3.Yes you can still be upgraded.
4. There is no unwritten rule but people have there own thoughts.