I have zero experience when it comes to cruises. I have been single and live alone since my transition, so take this with a grain of salt.
If I were in that situation, planning would be my priority. You are not just going out for an evening, you are going out for a week. So plan accordingly. What supplies will you need for the duration?
Plan for every day and part of a day.
What will you sleep in?
What will you wear in the mornings when you get up?
What will you wear if going for a walk on the deck?
What will you wear in the evenings, for dinner, dancing, or whatever?
You have the bikini for the pool. Are you comfortable wearing it as is? Or will you be more comfortable with a skirt or cover-up, as Danielle mentioned?
Once you have planned out every outfit, what happens if the weather changes? Will that still work, or do you need a backup outfit just in case?
I think you have a prime opportunity here. Just be yourself. I am most comfortable in jeans, a t-shirt, and tennis shoes, so that is what I wear. I would never be comfortable in a beautiful sequined dress, so I don't wear them. When you are comfortable, you can relax and enjoy yourself more. When you have a well-thought-out plan, that is one less thing to stress about. You are not trying to impress an audience; you are going to have fun.
Then, as suggested, use your solo trip to test your plan. Note what worked and what didn't. Tweak it as needed. Come March, you will be dragging your wife to the boat! Have fun with it. It should never be difficult to just be yourself.
Maybe your wife is just curious about how far you want to go. Will you wear fancy sequin and rhinestone formal gowns every day, all day? Or will the real you just want to hang out in comfy PJs when going for breakfast? She needs to see what the real you looks like to her. That is how she can make an informed decision about how she feels about all of this. The fact that she is open to trying it out speaks volumes about your love and bond.
That is special.