Is there a reason you are locking them up? Can you provide shelter in a paddock?
I understand if there is a dog/ fox problem but just curious.
The blackberries will be great. Mine LOVED milk thistle and any "gone to seed" plants from the vege garden. I also supplied 1st cut hay for them (usually Lucerne as we picked it up when we got a load of horse hay). I found 1st cut to be higher in roughage than the softer 2nd and 3rd cut. We found the goats useful as "cross grazers" as they like long rank grass that the horses don't like so much.
It sounds like you will have a great time with your goats. They are really easy to train to walk on a lead like a dog and we also trained ours to pull a little cart.