I think about starting a niche content project that would be filled with tons of highly hierarchical data.
What technology stack would be the most appropriate given that I'd like it to be open-source, simple, cheap to run and scale? Thank you!
Node.JS is a good choice in my opinion. It's new technology, but so was everything at one point.
See the question Node.js + Nginx - What now? for details on how to proxy Nginx to Node.JS.
Mongo DB is a good choice for highly hierarchical data because of the way it is, although I have heard PostgreSQL now has better support for storing JSON documents.
The fact about MongoDB is that it is FAST, and if data reliability concerns are negligible it would be an excellent choice. Another cool thing about MongoDB about this is that there is no "schema", you just make up what you want to store on the fly.
One con of MongoDB: You won't be able to query across that hierarchy of data as easily. There are others, but this has always been a big one for me.
My advice is always this: develop in whatever language you are comfortable in, and worry about the other aspects later. There is no point in being an architecture astronaut at such an early stage in a new company or idea.
In the future, please post questions of this nature on https://softwarerecs.stackexchange.com/
