[OhHeyItsE]

> Put aside what devs at your company may already be comfortable with

At your peril. Sorry, but it's true.

Any time there is something even slightly amiss it's going to be "Uh oh - looks like Mongo is giving us trouble again."

No matter what the real problem is a slam-dunk scapegoat. And your name is going to be forever attached to it.

Also consider how you're going to deploy & maintain the stack itself. Do you have an ops team that's familiar with deploying war files into a servlet container? Well now on the critical path to this thing going live is them learning how to maintain a new app server, language and deployment process?

That said, at the end of the day - all the tools, frameworks, and languages you mentioned are just fine, with some slight nuance:

DB: MySQL is fine, Postgres has some nice additional features if you need them: GIS, great scripting support, etc

API/App: Stick with the big ones (Elixir? C'mon...). Slight edge to Node because JSON de/serialization is automagic. Slight ding to PHP because... PHP.

Frontend: Who cares? It's going to be outdated in 6 weeks anyway.

Caching: Which ever one you don't have to maintain or think about. Did you choose AWS? Great. Elasticache supports Redis and Memcached.

PaaS: Whichever one supports all the features that you need.