Hello, thanks for this! I was searching on the forum about anything I can find helpful in terms of cross country trip prep recommendations and this post was the closest I can post under.
Planning my first cross country trip in June from west to the east (3000miles) with my 2019 insight EX. Currently has 17k miles on it. My questions are listed as follows, I'd appreciate if you or someone in this forum can help to this unexperienced cross country driver

(although I've been driving for 13 years, I've never driven a cross country before)
1. Whenever I drive my EX for more than an hour I feel numbness and soreness on my tailbone area, this may be caused by the lack of lumbar support I assume, so I am planning to get one of those lumbar support and even a neck support from amazon, any recommendations for a long road trip like this?
2. What checks/maintenance would you recommend before hitting the road? For ex. even if the oil change is not due by the time I am hitting the road, should I have it replaced still? What about tire rotation? Or any other mechanical maintenance/check recommendations I should be taking care of rather than it's regular maintenance schedule?
3. The car will be loaded with luggages during this trip, possibly with the back seats folded down all the way to increase loading capacity of the car. What are the things I should be considering when loading the car so that I don't have to use Sport mode all the time

to gain speed on a freeway?
4. Does anybody recommend underbody coating for east coast? The car will stay in the east during winter and since it's a CA car, I prefer it to be protected when it's in the east coast. To mitigate any damage to the underbody of the car, I wonder if people here apply any coating beforehand.
5. I usually use 87 unleaded, but during the road trip, is it also recommended to use the same, or can we upgrade it to 89 or 91 even to increase performance of the car?
Thanks in advance!