Simply, a node is a collection point for content. I look at them as cupboards you are building to organize different things (content). The type of cupboard you build depend on what you want stored in there: cups, can food, plates, etc.,
Node types are only needed if you're designing something to sit within the node tree, like a forum or a page. If you're not trying to do that, then you don't need to bother with them.
Content types are really just used when you want to involve frameworks that are content agnostic, such as like or report handlers. These are situations where you use basic frameworks and extend them with content-specific handlers. The only time you need to create a content type is when you start delving into that.
I don't know the details of what you're trying to do, but your node/content type breakdown sounds reasonable.