I don't believe there is a good answer to this as details are missing. What scale are you trying to get to? What level of concurrency? How much state and how often is it accessed? And what are the skill of your engineers.

You could write a rails monolithic app on postgres if you're building an internal application 100 people will use. Or you could use Akka and Scala with all state in memory backed by an event journal stored in cassandra.

IMO Ruby, Python and Elixir are perfectly suitable but the last languages I would choose. I've been working with elixir for the last 1.5 years and have decided I don't really like it. I'm happiest writing scala - I get more done faster and less bugs make it into production. Event sourcing and Akka cluster allow some really interesting patters that move state into application memory. But those technologies require a much different, more involved skill and experience set to lead.

I'd probably be using Go or Scala if I had to start a tech company in a small city. Scala if I were in a large city with talent 100%. There is evidence that Static typic improves speed of delivery and it's easier to refactor/maintain. And it's faster (generally). Both languages are much more widely used than elixir.