We measured a course on a college campus a couple years ago (CT16048JHP). The RD assured us that there would be plenty of volunteers. The map of the course included the location of 34 monitors. These locations could have been cones (although a much more precise location for each would be required). The RD reported great success and no problem with volunteers. That may be something you can do to ease runner confusion on race day.
As for a turnaround spur, maybe one of the wheelchair ramps that connects to a sidewalk? I have found that it is way better to get the course as close to 5K as possible on Google Earth before measuring. On-site course design is highly inefficient. I recommend you put your turnaround spur into the map before measuring the course.