I have done many public speaking engagements in settings where meals were part of the program. Avoid spacing round tables widely apart in an attempt to fill the available space.
Distance makes audience involvement and participation much more difficult.
Empty room space could be filled with a decorative divider of some sort. Again, distance is a great barrier to speaking and interaction. Consider allowing the speaker an option of speaking areas. Most public audiences like being closer to the speaker too. You would not want them seated behind the speaker during the program.