Andrew Mayflower wrote:Re-reading, and to more directly answer your questions, it's less a matter of time that the sheep or goats are on the land and more a matter of the effort you put into prepping the ground. Since you can only work on so much at a time, the animals will be used to keep the underbrush from re-growing in the areas you haven't yet been able to get to, and maintaining the areas you have completed until the cattle are ready to move in.
The lack of local goats is probably more a factor of local convention than goats per se not being suitable to the environment. People raise goats from the hottest parts of Africa to the northern reaches of the USA. So there is likely a breed that would work for your application, but it may just not be feasible because nobody around you has them.
I don't think pigs are much of a threat to large, established trees, but they certainly would be to saplings and immature trees. How effective they'd be at clearing depends heavily on the breed. A type that loves to root through soil for tasty tidbits would be the kind you'd want, rather than a grazer like kunekune.