Additional Insureds, Certificate Holders, & Crew Members

How many Additional Insureds may I add to my General Liability policy and how quickly do they appear?
CGL - How do I insure the work of multiple people with Thimble?
May I swap Named Insureds before a policy expires?
CGL - What is the difference between an Additional Insured and a Crew Member?
CGL - How do I add or edit an Additional Insured on an existing General Liability policy?
CGL - How do I add an Additional Insured to a new General Liability policy?
How do I increase the number of crew members on my General Liability policy?