Video tape your PDI. If you have kids, get a babysitter and leave them at home during your PDI. Do not hand any money over to the dealer until everything is fixed to your satisfaction. Your money is their motivation. Once they have it, you go to the end of a very long warranty work line that will take weeks to months to get done. If you have to delay your trip then delay it, you will be thankful in the long run. Make sure they demo and you return the demo on everything. If it turns on or off, opens or closes, moves up or down etc you want to practice it with them. Make sure you learn how to use your dump valves (look up geo method
for tank management). Make sure the water tanks fill, water heater works, faucets run and no leaks. check the roof and all caulking etc. Make sure they demo how to winterize and dewinterize your trailer (water heater/pipes etc). This will save you money and time in the long run. Have them show you how to properly hook up and unhook your trailer.
Take your time. Expect to be there for a long time. A good PDI should last at least an hour. We were there for over 5 hours making them fix things before taking possession with this trailer.
As for what will you mess up? Your guess is as good as mine but we have all made some pretty good mistakes. That is how we learn. If need be, ask a neighbor for some help. A suggestion for backing up... get a set of walkie talkies for you and your co-pilot (spouse). This will prevent yelling and annoying others. Learn to direct by saying drivers side/passenger side instead of left/right. It decreases confusion. DH will direct me by saying things like tree 3 feet back drivers side or go more to passenger side. He will tell me to slow down as I get close to a stopping spot. Working on communication is important. Remember, you will not always be happy with each other during backing in. Take deep breaths and remember you are trying to help each other.
Also, make sure you buy a water pressure regulator to prevent too high water pressure from destroying your water lines (cheap at walmart), and a surge protector that protects from over/under power problems. Very important to keep your electric and appliances from getting destroyed by pedestal power problems.