Goats are social, so you'd definitely need more than one in a setup like that. You will probably have to add electric fencing to keep them in, at minimum unless they're tethered, but if they're tethered they shouldn't be left unsupervised all week.
Honestly, I don't think it's a good idea to leave any large stock unattended that long for water reasons. It's pretty easy for an automatic waterer to malfunction and unless someone is checking daily to see if it's working, that's just a terrible way to die.
There are people you can rent goats from for brush clearing purposes, and they come out and do all the care and stuff so that may be a way to go.
Depending on the type of brush, geese may work too. That's a huge area, but they're really efficient at stomping down tall grass, eating the seeds, the grass, etc. They're grazers really.
Most things you get will be vulnerable to predators. Guineas are pretty dang hardy. A flock of geese may do okay together. Depending on the climate, you may need someone to go out daily when the weather gets cold to supplement them with grain or something.
There are some varieties of sheep that may help with your brush too, depending on what you're trying to clear. You could probably get by without an electric fence with them (unless coyotes start to pick them off). Also, you could avoid the problem of winter care by getting a bunch of spring lambs and then put them in the freezer come fall.