Please allow me to voice my two cents worth.
Regarding a format, scan some podcasts online and find one you like, or conduct a poll here in a forum if you are unsure of what forum you want.
As far as topics, I see well over 100k questions and many more responses in the various forums. Pick one and use it to discuss in this podcast. You already have the problems and answers right there

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How often to have a podcast? I would say one a week to begin, maybe doing an occasional extra one if the notion strikes you. As you become more comfortable you might want to increase their frequency.
And here I am talking as though there will be only one host. Whoever the host is might have guests on from time to time, starting with other knowledgable people from right here on TFP.
The most important thing to keep in mind is the value given to the listeners. That is the difference between a podcast that is so-so and one that the listeners cannot wait until the next broadcast.
One last thought. Just keep in mind, there is never a face too ugly to host a radio show-[I heard that somewhere long ago.]. I think a podcast for the interested public would be awesome.