Ooof... right that's a very complicated position. You'd need a forum or microblogging platform that can be hosted to convenience (cheap price / gratis; ideally away from Nine Eyes and from Iran eyes). As for the media storage requirement, if your community is going to be media-heavy, that's a lot more damage on the long term: either you host the media and run the risk of delivering a lot of private info when caught (most media uploads are not sanitized for privacy, nor people know how to do that), or you don't host the media yourself and count on the users uploading it to somewhere else that you'll have to "moderately" depend on.

If I were you, I'd think hard and long whether media (especially heavy media, such as videos) is that much important as to have to do the hosting by yourself or whichever group you are organizing. Any way you can find of getting out of that hurdle will be good for costs, for mental health (moderation etc) and for security (as I mentioned above, as well as other factors). Torrenting heavy media files or going Cuban aka.: distribute through a physical network of hidden flash drive caches, might be available options.