What would you do first with a new (to you) expedition?

[Trainmaster]

You may want to change the idler pulleys and belt if it looks like they are original. Any of those leave you stranded and most folks don't maintain them.

 

[Dahammer]

1st I would do LOF, antifreeze flush, and brake fluid flush.
Plus I would get a copy of the owner's manual for the vehicle. In the manual mostly on the back pages is the maintainer guide