I would argue that the fact that Arrow has been integrated into so many projects over the last year is proof that a separate project made sense. Dremio, PySpark, Pandas, MapD, NVIDIA GPU Data Frame, Graphistry, Turbodbc, ...
We considered starting a company in SF a couple years ago. I'm glad that we decided to instead start it in Mountain View (http://www.dremio.com). We're able to attract very talented people from San Jose, Milpitas, Redwood City, etc. where rents are a bit more reasonable.
Unless there's a really good reason to not split it equal, I think it's better if both founders have the same amount of equity. Otherwise you could create unnecessary tension which is the last thing you want at that early stage.