You'll have problems with land owners. We drive around now and find these pockets of about 5-12 homes on what used to be a farm, and no livestock. They won't like elk tearing up their lawns.
Also, not enough food. Right now hunting keeps the local deer populations low enough to survive the winter. Deer compete for food with each other. Single deer have been kicked out of the herd. Coyotes and Coywolves compete for food, too.
Recently small herds of Przewalski's horse were reintroduced to Mongolia, where most of them are extinct. These animals were bred and raised in zoos. Of the two herds left out to winter, one almost died off, and the other, let out on a preserve with plenty of fodder, mostly survived. ALL of this should be carefully studied before it's done, and maybe should be raised on ranches. We have the owner of about 50 acres, some 10 minutes south of us, who bought a horse property, then put in super strong fencing and are raising Buffalo! They do fine, BUT it's on what is a closed down garbage dump (with hills) and they provide water, but the hills give a natural wind barrier. THEY TAKE CARE OF THEM, instead of expecting them to fare for themselves.