Just wondering what the requirements for banner towing are...

A waiver from the FSDO, which you are unlikely to get as a 145 hour
private pilot.

Refer to 14CFR91.311 Towing: Other than under 91.309.
No pilot of a civil aircraft may tow anything with that aircraft (other
than
under 91.309) except in accordance with the terms of a certificate of
waiver
issued by the Administrator.
91.309 cover glider towing.

Michael