3. Can a TSA agent demand to see your driver's license and refuse to let you leave the security area until you provide it?
Don't ever carry your DL as your ID (or if you need to have it with you, hide it deep within your wallet) - take your passport instead and make up an address if they demand one - I've done that a couple of times.
5. Under what circumstances can they refuse to give you a complaint form? 6. Who would you file a report with?
They can't refuse to give you a complaint form - but they probably don't have them. Keep a notepad and pencil with you and take down names, badge numbers, date, time, etc., etc., etc. Send a letter with all information to TSA in DC, copy the local FSD the general manager of the airport, your airline, your congresspeople and consider adding your local ACLU chapter.
You're not going to get diddly in response from the TSA, but if you make certain you copy every entity you can think of it gives a bit more credence to your complaint.