With so many people on this boat, even with sign ups it may get full. If possible we may want to create a few distinct places, able to be combined for group practice.
It is. Which is why I expect they will also have a decent number of combatants. To prevent a slaughter.
I could set up some basic wards and safety magic. For example, most boats with magicians aboard will ward against fire in my world. Forcing them to stay in the corridors sounds best. But unless they have information on us, the guests, and what we have they might want, I'd expect them to go for people (if there) or to valuable ship targets.