All good questions and so nice to have someone asking! First, ask the venue if they offer hearin assistance. Larger public access Venues should by law have hearing loops installed or FM systems available. Be sure it is well posted what is available. Or better, have the headsets available at check in for your event. Many church halls have this too.
2. You need to make sure there are microphones for and speakers, and extra ones to pass around in the audience for questions or discussion.
3. Many using Hearing aids have a remote mic they may want the speaker to wear, or to place on a conference table, particularly if there is no hearing systems in place. You could also borrow a Roger multi mic for this purpose from your state program which lends out assistive devices.
4. Be sure the speakers use a microphone correctly, repeat questions from the audience, and speak a normal rate and speech. Not too fast!
5. You could either arrange for a CART reporter, or use speech to text software that you project for everyone to see what is said translated into text.