You can add as many as you'd like in all of the free and paid plans :)
Regarding who should get admin access, ask yourself:
Who will talk to the employees to find out what makes people press green? Who will take action to try to fix the red? And act on the results on a really red day/week/month?
This person should have admin access so s/he can check the mood results on a particular day, receive weekly email updates and verify how the Mood KPI is developing over time.