Yes, under 25HP you should be all set with the 6. Don't think you need to remove the prop though.

Also, don't be afraid of the test. If you have any common sense on the water and a little bit of studying you will pass easily.

The only thing that I had no clue about was personal watercraft (jet skiis). I think they should make that separate and harder forcing them to take a driven water test, drug test, and make them do it twice. Can you tell how much I like those jet skiis? ;)