My mailing address is a PO Box. Should I enter my property address where I reside as my principal/physical address?

Use the address you want the IRS and state to use if they need to mail you a letter or a check.

You can enter a PO Box in the Personal information section.   You should use the address you want mail to be delivered to.   There may be places you need to enter the physical address, such as a state return, or if you are taking residential energy credits, but you will be prompted to enter a physical address when one is required.    But PO Boxes are fine for the taxpayer address field on Form 1040.