Pygmy or Nigerian Goats
Wow, you have a very nice city! Even when i had a 100' x 250' lot, I still couldn't legally keep that stuff, you need at least 3 acres where I am. In addition to the kennel and shed, they would need an outside pen, maybe 50 x 40. As you said, the kennel should only be for when you are not home or at night. That way, when you want to keep them contained, at least they aren't cooped up in the shed and have some room to roam around. Then let them out in the pen during the day. 20 x 20 isn't a good size for them to stay in permanently. 40 x 50 is a good size for the pen, in addition to the kennel. That would give them sufficient room to run and play. Don't skimp on fencing, either. They require strong fences. I don't know what you were planning, but use 4x4 or 2x4 field fencing attached to some strong posts. That is a must. Goats can be escape artists, and will escape from weak fences. Make sure there are no gaps, either. If I had to plan out a goat pen, I would use 6' wooden posts 18" in the ground, stapled to 4x4 or 4x2 field fencing, with a strand of electric wire on the top. That would be the ideal setup. Expensive, but worth it in the long run. You skimp on fence, and the predators will get in, and the goats will get out. Never a good thing. Raccoons can kill smaller goats, which is why the electric wire is necessary. Luckily they only come out at night, and you can have them locked in the kennel with access to the shed.
As far as breed, it is your choice. Both are nice breeds that could fit on your lot. If it were me, I would go pygmy.