Anyone go through the process of obtaining a COI from the Coast Guard?

Hey everyone. I am trying to establish a scuba diving boat charter business in Florida and have been trying to learn the process of obtaining a COI and all that is needed to run my business legally.

I've spoken to the coast guard office as well as a few captains and other people that have been through the process but it still seems fairly confusing. The biggest questions I have would be:

1. Is a COI even necessary to run a diving boat charter business?
2. What does the process look like?
3. How much better is it to purchase a boat that has an existing COI than one that currently doesn't have one? (We have identified two boats that fit the bill. The one we like a lot doesn't have a COI, the one we may have to settle on currently does have a COI)

Thank you for any and all feedback. Any other information that you all think might be relevant is definitely appreciated as well.

Thanks for the reply. Is that 6 passengers including myself and crew or 6 passengers and then additionally myself and crew?

Thanks for the reply. We may go that route.