Elyte before the trip,
DONOT UNLOAD, No reason for it, and very dangerous.
Stop every 4 hours or so, park in the shade offer water and fiber feed, like soaked cubes or beet pulp. take a half hour to hour and headback out.
A trip that long I would look for a campspot to park and sleep, in that case I would unload and give hay and water and elyte. repeat the next day. Id look at about 500 a day as reasonable, if you can handle more horses be ok, just watch the weather and time your routes so you miss cities and traffic jams during heat of the day. Carry plenty of water and presoaked fiber feed.