I use Freemind Mind Mapping software to store all of my GTD lists. I have a separate mindmap for each list (i.e. In Tray, Next Actions, Projects, Project Support Material, Someday, Tickler Calendar, etc.)

GTD has certainly freed my mind up, but I'm stuck as to where to file next actions. How many actions to have in the Next Actions list and how many to specify in either Projects or Project Support Material?
Should I simply put a single next action for each project in the Next Actions list (so I can safely empty my mind of what to do next)? Alternatively, should my Next Action list contain all of the next actions I'm aware of and collate them under project contexts?
Also, what is the recommended way of specifying contexts in Next Actions?