I would leave chat alone with a group that large. You can provide that functionality to have an open communication between participants and possibly presenters/hosts for quick exchanges, but don't rely on it for question and answer functionality. The Q & A pod will queue up all the questions that are asked in it and you (or other presenters/hosts) can answer them while keeping the answers associated with the question and have the ability to reply publicly or privately. All questions are asked privately and are not seen by other participants, so duplicate or inappropriate questions can be easily removed or ignored.
Polling is also good to keep the responses in a controlled evironment.