Hello bloomer
Yes goats will be quite happy on a steep slope- worse thing will be that fencing a steep slope won't be much fun! And that anything they have out in their yard/paddock, will end up at the bottom of the slope....
Shedwise- I would always say get/make one as big as possible, goats have a way of expanding. But,that said, you have to think that you could have as many goats as your two adults, plus say two kids each. Then- what are you going to do with the kids? If you want to keep them- rear them for meat maybe? Then you might still have them until they are 8-9 months old, and therefore getting bigger.
Our adult females get a pen on their own of 6ft by 6ft. If they are sharing with a friend, they get one and a half pens, so 9 ft by 6ft. But you need room to split them up if necessary, so at least maybe an area 10ft by 6ft which you can split in half.
Then Happyhippy is right, you need a space to store food, and to milk indoors. My sister is managing quite nicely to keep her goats in a double field shelter, so 12 by 24ft. But she has 4 milkers, 3 goatlings, and 3 kids (she is running out of room!), plus room for feeding and milking.
I would think you could manage with a 12by 12 shed, or even 10 or 8 by 12 if space is tight. But another small shed would be useful to keep some hay and straw in. You'd want to keep a couple of bales of hay in stock, just in case of bad weather in the winter.
If I only had a small outside area, I would be inclined to make a yard- even just 6 by 8ft which is paved, just so they have an outside space for exercise which won't get muddy, and then the rest of their outdoor space as whatever you have.
In terms of when to get some- I would suggest either in the autumn, get something in kid maybe, and a companion, which could kid the following year. The ideal would be to have one goat kid each year. Or to wait until spring, when you could get a goatling and a kid, or if you are brave a milker and a goatling.
You are welcome to come here for milking lessons- I may need you to visit anyway as I have a fencing issue!
What breed are you thinking of?
Beth