I have goats and have done some
land clearing with goats and general herding.
They LOVE blackberries and alder. I agree with the predator control though or you will not have them very long. Goats and sheep without proper protection are like
chickens - everything eats them. Goats' only defense is inaccessibility - whether by living high in the mountains where nothing in its right mind will go...or using humans and their fences/buildings and Livestock Guard dogs. Even a horned goat really can't fight off a predator. Especially a bear. I would also read up on poisonous plants. Stupid babies and goats who are not familiar with the
local plants will eat poisonous plants...and then you must deal with sick and dying goats, and then decide whether to replace the dead ones or continue the year with the number you have left.
For 3 acres...I think you need 15 goats to an acre to clear land. That's adult goats, not kids. I think that's what I read... If you are skilled at butchering, bucks would work, but you need to keep the hair off the meat. Baby wethers may not get very far at clearing and will not be very adventuresome without having an adult goat leading them. I speak from
experience with this one. If I were going to do your
project, I'd pick up a couple of adult wethers or does (who didn't make the cut as milkers) and keep those longterm to be your lead/trail boss goats to get the annual acquisitions to browse efficiently.
Goats, especially tame ones, adapt very well to being brought in at night and going out to browse during the day. It plays into their ancestral Ibex instincts. Ibexes (and domestic pastured goats) have their "safe place" where they are safe from predators (high rocks or barn/shed) and then go out every day to migrate around their environment to eat. At dusk they return to their "safe place" to sleep. Some also like to come to the "safe place" to take a midday siesta. My bottleraised goats particularly like it if I go with them as I've imprinted them on people so they see me as the "senior/lead doe". You could conceivably fence the entire area and just lock them in at night. Maybe fence your house away from them or they may take to sleeping on your porch for their siesta...or your house if you left the door open.
Fences - 4 ft fence is generally adequate. Swiss breeds are the most athletic and occasionally require higher. Nubians and Boers are generally quite lazy and placid and I've gotten away with 3 ft, but I wouldn't in a predator-heavy area. I personally prefer 4 ft wire mesh with a strand of electric at goat-nose height. If you want to eventually divide up the areas, I highly recommend Premier1's portable electric mesh. I just bought some this year and it's a game changer. Quick and easy to put up by yourself.
Polled goats are extremely rare. I own two polled bucks and leasing a third in hopes of changing that. I believe you mean disbudded (born horned, horns removed as kids). Breed matters less than how the source herd is raised. Although for meat and land clearing, I would avoid miniature goats...they just can't eat that much and they only get so big. Look for herds that don't heavily grain their herd. If they have their goats out on pasture, even better. Boers are good for meat, as are Nubians. Nubians are easier to find as disbudded vs horned. Lamanchas often have decent muscling also. They are naturally "earless" and look a little strange to a non-goat person. Saanens get big, but they are mostly bone.
Do
NOT source them from a salebarn. That is where culls go (cull = unwanted, unthrifty, diseased). You risk bringing home sickly and diseased stock, and some of those diseases infect your soil to infect later goats (or sheep, sometimes
cattle if you ever want other livestock). Even if they didn't arrive at the salebarn sick, they can pick stuff up while they are there. Wethers are probably the cheapest (
dairy wethers anyway...Boer wethers can be expensive) and can be bought from any dairy breeder for very little money in the spring. I
sell mine for $50/head. If you bottleraise, you can often get them at a couple days old for not much more than a song if you find a dairy or a serious dairy breeder. You may avoid telling the seller that you intend to eat them...just say you want brush clearing goats. Some people don't like to think of their "babies" getting eaten.