You have lots of time to think about options and additions:
Are there any other "secret menu" items like this that I should add that are not really advertised by ATC?
If interested you may consider a Maax Air fan, nice option to have vent open when raining or driving. Caution due to some issues with little tolerance to voltage increase,may need a voltage regulator. Sales often through Camping World.
Roof racks are in short supply, but should be installed by them.
Exterior and interior LED lights I didn't like, so ordered from Eshine and ledbrightlights
Decide where your dinette will be
Decide location you want all the wires to come in.
Location of switches for lights if no cabinets available.
You can add any length to the camper up to 8'
As Goingoregon suggested, propane door.
Almost anything can be customized
As one member once said, the camper is just a glorified tent, and omg how expensive the options are
Have fun(spending your money)