Earlier quoted context omitted.
1. SF for now. 2. Yes, eventually we'd like to have multiple groups in the same space just for this reason--I always think the interdisciplinary stuff is underrated. 3. Some of both, probably, but mostly we want to support people that the existing system does not support (e.g. people that are not yet famous)
FWIW, two (partially self-serving) suggestions: 1. Try set up a lab in Cambridge at some point down the road. 2. Pay particular attention to CS theory: it's (arguably) high-impact and very cost effective --you can practically fund an entire generation of researchers in a subfield for a fraction of the cost of, say, a major interdisciplinary initiative. See for instance what the Simons foundation is doing at Berkeley[…
MA or UK, though? Both would be awesome, I think, but I don't believe YC has any offices outside the US at the moment...?