It’s far too situational to give a blanket answer. I run a 15 person startup, and my preference is product focused people because of the breadth they can cover. However, we have a number of people who aren’t that way and are just good developers, which is great. My sense would be the narrow/deeper technically a space is, the less preference there is for product focus, but again just my personal guess.
This is quite cool. One suggestion would be to have the pronunciation listed in addition to the kanji and audio (at least when I searched I didn't see it, so the only way to learn to pronounce is to use audio). Do you know of something similar for Chinese by any chance?
This assumes that you're power generation always matches demand through time. If you had a sudden spike at night that you don't usually have (like in Texas where people kicked on their heat unexpectedly) and you were using solar, the mismatch would exist and you wouldn't be able to meet the load.
1) most have RSS (the three you mention all do or it's one jump to a site that enables)
2) most other social sites are themselves collections. If you got big enough, yes they'd mind, but not to start. Hopefully by the time they mind people are submitting to you anyway.
3) seems like a stretch, but ianal, given they expose RSS or APIs currently