My first question is why hire a public relations person/firm?

Promote yourself.

Talk at Meetups + CoWork Spaces + Conferences. Where ever real humans show up in the flesh.

Depending on the content of your podcast, you might look into Alex Carrol's Radio Publicity course. Alex is the only guy I know who does Radio Publicity like I do. Well, Alex is the only guy who's ever shared the secrets in print. Most people successful at PR, especially Radio are rich from doing it + would never sell their services, as they'd lose money selling services.

So... the best PR people... well... you'll never hear about, because they'll never say what they're doing.

Other considerations for you to research.

Traffic Oxygen

Author Platform Rocket