I have done many many trips like this (business and vacation) but recently did a cycling Italy coast to coast trip - amazing!
When I travel for vacation, I’ll have a few drinks on the plane (I’m going on vacation!) and sleep if I feel like it. The key is to stay awake when you are at your destination until it is sleep time. Normally it’s no problem because there is always lots to do when you first arrive and everything is exciting. Definitely don’t nap, stay awake and keep busy.
Don’t worry about eating anything special - it’s vacation!
I will take melatonin if I’m wide awake around sleep time. Label dose 1hr before I want to go to bed. If I forget, I’ll take it when brushing my teeth. It helps get you get to sleep quicker but won’t necessarily keep you asleep. As long as you don’t stress, it will be fine
Go with the flow. It’s a vacation not an A race. Stressing over the details will cause more problems than having a relaxed attitude.
If it was an A race you would want to arrive in plenty of time to adjust. Everything will be fine. No need to experiment with ambien etc for this in my opinion