Aside from that in Haskell the type system isn't usually a restriction. Experts in Haskell tend to use the type system to guide them towards a correct solution.
I'm not sure it possible to say that we couldn't have built something quicker in another language or stack. What I will say was that the underlying abstraction that we built our system on (streams of events) is very well suited to a Haskell implementation, and I can say with some certainty that building a solution that is as "correct" as the one we built would have been extremely challenging. The code also held together for longer than has been my experience in some other languages and communities.
Yes, absolutely. It's amazing how overlooked this fact seems to be, by many. Languages aren't that hard to learn, so excluding the really awful ones (e.g. Java for anything other than code that has to be on the JVM and has to be fast) the "familiarity" aspect is minuscule. Programmers learn new languages quickly. What does matter is the community and the quality of programmer you'll attract based on the tools you use and the signals that your tools send about who makes decisions.