forget a spinnaker - use one of these "portable downwind wind catchers"
Kidding aside: "My main question is what point of sail can the spinnaker be used? "
depends on the cut but reaching is more for screechers and code zero type sails
this is based on 2010 sail tech - i am not more current that that but I own an Olympic Tornado prototype spinnaker that was tested for the 2008 Olympics. lots of teams were testing spins that could reach higher but i don't think they were utilized
(we used to get used olympic and other race tornado sails from Red Gear Racing)
i don't think any team had success with these