Unfortunately, you can no longer just walk your goats along lanes etc. to allow them to eat verges. Personally, I would never do this anyway, as it encourages the goats to think they can just go over the fence and go off and graze "their" verges!! But, there is nothing to stop you from collecting leaves from safe trees, which goats love, and feeding them to your goats. (I do this) I would be cautious about picking things at ground level, as you just do not know what may have been sprayed on them, and of course pollution from passing traffic etc.
Although I have sheep, I do not allow them to mix with the goats - the exception to the rule being my ancient shetland sheep, who has been here years, and he shares a paddock with the pygmy goats.
As to how much land, well, this all depends on what sort of land, how many goats you have etc. Goats are browsers, and that means they would choose trees and bushes over grass, so whatever land you have you need to fence it well!! Some breeds will stall feed, which means they do not have access to green feed, except what is brought to them....obviously more work involved.
Ideally, you would need two fenced paddocks, so that you could rest one, as in the winter months, the rain and snow can make a muddy mess, along with you, and the goats waking about. Most of my goats tend to be kept in over the winter, so the field gets a rest, and it also stops them getting foot trouble from the mud.
I have to say keeping goats is not cheap - especially is you have numerous. An adult female can eat an alarming amount of hay!! I feed hay in racks all year round, as I do not like them going out on summer grass on empty bellies, as this can lead to things like bloat. To get the milk, you need to feed plenty of goat feed etc......all costly.
As to eating goat meat. I keep Anglo Nubian goats, and was persuaded to try some cooked meat from that breed. I thought it was really nice and not a sign of any fat at all. As with the milk, you need to feed the meat goats to get the weight on, again it can be costly,.
It is sensible to try the milk, cheese, and meat before embarking on goat keeping - would be a shame to get the goats etc. then find you do not like the meat or milk!!!