All, just curious and looking for opinions. I have a client

Hi All,
just curious and looking for opinions.
I have a client who wants to build a type of testimonial site.
This will work with multi-site well because he has different groups that will have their own site to post to. He wants the sub sites to feed into the main site and be searchable.

My question is that he wants a responsive theme and wants the people to be able to post from the front end. Simple is better.
They will have to be registered and logged in to post.
What are the best tools/plugins to accomplish this?

Can this be done with the directory plugin?
What about the classified plugin? Can it be modified to work?

I'm open to all suggestions.
What is the best simplest way to lay it out?

Thanks for your time.
Proud to be a WPMu Dev member.
Richard