If you only want the goats as pets/pulling a cart, then castrated males are the most suitable, and you will be able to pick those up cheaply. The larger dairy breed boys, such as British Alpine, British Togg, Anglo Nubian are a good size when castrated. I can vouch for their size as we have 3 very tall (almost as big as our small pony!) BT castrated males.
Have to say, although we have carriage ponies., I have never had the desire to put the goats in a cart!
As to the scrub clearing - a word of caution. Yes, goats do eat brambles, nettles etc., although they prefer tree branches. Do check there is nothing that will poison them there, and also I never let my goats eat anything prickly, as they can get scratches (female goats can hurt their udders) and I have even known goats get eye injuries through grazing such land, and one got a huge abscess with an even bigger vet bill through gettingh a thorn from a bramble bush in its face
Our goats are out with the pigs (well the pigs are fenced in,) but goats never bother going near the pigs. I do not think I would put them actually together, mainly because the pigs would dig all the grass up!!