I think it's good to have separate Welcoming Committee members so newbies have someone they feel comfortable approaching with "dumb questions". You know, the stuff you feel you should know but can't figure out when you're new to a forum or don't want to spend a lot of time searching for?
I guess Reviewers would be people who make suggestions to people in the Gallery? I think to be a Reviewer you should be an established designer yourself. I've seen newbies come to the Playfish forum who aren't very good at designing themselves, yet they're in other threads telling people what to do with their restaurants. It's kind of sad! Not everyone can win Restaurant of the Month so don't think you necessarily have to have won a design contest to be a Reviewer but you should be articulate, helpful, and have a lot of experience with the game. Maybe people can apply to be Reviewers and submit 3 of their best designs so you can decide if they're qualified to help people with their restaurants.
Olivia is a safe trader and knows a lot about that stuff so maybe she can help you with setting that criteria.