Do you need to show your boarding pass at TSA check in

Yes, either by phone or printed. Your ID/Passport as well

Yes

Yes, unless you have Clear access where the boarding pass is checked at the Clear station.

Yes. Boarding pass is a mandatory thing you need to show to the TSA officer before entering security check. You can have a printed copy or show on your phone. You will also need a valid form of ID (US driver's license, DMV ID, or passport).