Did you have trouble hiring Scala devs? And if so, do you think the language benefits outweighed that. This is my main concern choosing to build new ventures with Scala.
Totally. I think the right way to pick a language for a startup is to find some smart, experienced devs to hire and let them pick (modulo reasonable business constraints). The popular languages all can do a wide range of things effectively. The more important factor for productivity is how well the team knows and likes the tools.
As an example, we know that PHP is a "fractal of bad design"[1], but I can't deny that Facebook as a business is doing just fine.
2.) When founders ask me about what language to choose, I tell them: "Choose one where you easily find developers, then you can't go wrong".