What if author don't have idea about a particular topic. For example, there are topics I am good at and there are topics I don't even have idea about and can't offer nothing.

My vision would be that if this works out, other blogging teams could start to cover other topics. Of course, one of those other topics could just be a sort of "general commentary" where people write about any topic that interests them. Not sure if that would be a good choice for a first try, but it might be worth considering. This is related to a point that @o1eh and @danmaruschak both raised, that it would be difficult to find enough people with a common interest.

Thanks for the feedback!