Hi there
Certainly sounds like you have thought this through thoroughly, and done plenty research, so well done. Cattle are great, but they are larger than goats, and therefore the risks of hurting you if they get upset at any point are greater, and therefore handling systems have to be available to deal with any potential problems, such as requiring vet visits, restraining them for injections, etc. Goats are quite similar in many ways to cattle, but are perhaps easier to get into.
We are in Aberdeenshire and have Saanens, who are (

) in kid to a Boer. We are aiming to have the crossbred kids so that the males can go for meat, and the females will still be reasonably milky for a bit of milk for ourselves, but will be a bit hardier than the Saanens. At the moment, our goats go out during the day, with a field shelter, and are in at night. Kinda depends how enclosed your field shelter is, and how easy it would be to muck out/keep clean and dry as to whether they could live out with the field shelter only, but if you have a stall available for rougher weather that doesn't sound too bad. They do graze a bit, but are particularly keen on the rough weedy bits at the edge, and the tree branches we throw in for them, so your grass plus rough ground sounds ideal. The fact you haven't had sheep in a long time is great, as there will be few worms on the pasture, as goats are more susceptible to worms than sheep as they are less designed for grazing. Ours learned the electric fence last year, though the first few times they shocked themselves, they just ran through it. Once they realised it hurt, they kept well clear, though occasional ears touch the bottom wire, and they would jump. It was mains powered, so it is well worth making sure you have something with a good zap!
Meat kids certainly don't have to be raised indoors and sent off early, this is a model that works for some people, similar models are often used in lambing, where people lamb indoors around xmas/New Year, keep the lambs indoors, fed heavily on concentrates and sent to slaughter early to hit the Easter markets and get good prices as supply is low. There is no reason you shouldn't fatten meat goats slowly on grass in a similar fashion to later lambers, and if there is dairy goat in them, this is likely to be the method of choice as they will grow slower.
If you wanted to come and visit, to see our goats, and how we do things, or ask any questions, just drop me a message, we're in Banff, so about a couple of hours from you.
If you were interested, we may consider selling one of our nanny goats (we have two two year old, first kidders, or a more experienced goat, who has kidded and milked previously) with kid(s) at foot, after they have kidded around April time, which would give you a nice little starter herd, and the kids would take a lot of her milk so you could milk off a little as you required without having quite the demands on your time that a milker who has no kids would have. Price would depend on how many kids she went with, and whether they were male or female. The females can be registered with the British Boer Goat Society as up to 50% Boer genes, so this can also affect price. If you take a look at the British Boer Goat Society, there are usually a range of goats available for sale, so you can get an idea of prices etc.