You don't want to overstuff it trying to appeal to every single fanbase out there. This is an anime site. First and foremost, this is an anime news site; so its well and good to stretch beyond that but don't go too far. It's much better to do something well that only a niche will listen to and love than something everyone just listen to and be indifferent about. (Though getting everyone will always be a struggle).
What podcasts, btw, are people currently listening to? That might give us an ear for what individual people are going for. If you're not, and want to contribute, you should start listening straight away.
(I post cos I care...)
OST, due to the nature of a podcast, could be good. (Though you don't want to separate every part of anime to different people, then you'd have people reviewing character designs and background art...)
If/when you wanted to get bigger, a video podcast could be done for figures. Along similar lines, you could always plaster video over the actual podcast itself, tbh and then stick that on YouTube - would be like an anime version of all them Machinima videos.
Possibly presenters need to work out a schedule too. Scheduling will be hell.