My main question is whether it makes sense to begin with node.js as a complete server-side newb. Is JS/node.js a good choice to start server-side web-programming from scratch?
I do lots of frontend work, namely HTML, CSS and basic JS. I even wanted to start with Rails but always had the feeling that not knowing what is going on behind the curtains makes me completely uncertain about the framework - it was just too much "convention over configuration".
My hope is to learn JS in general and dive into node.js right after that. I don't know, however, if this is a good approach for a person without any server-side experience. When looking at existing node.js topics and discussions, the used terminology seems to require lots of knowledge about how servers work in general.
Have no fear. Programming is all about practice and you will do mistake while writing code. But, that is how we all have learnt. Whether it is Ruby, Javascript (via Node.js), or any other language: certain aspects of programming are common and you will get familiar with things specific to that particular language over time. Being not able to remember a syntax or convention is OK. Just have reference material on your side. In fact it is encouraged to tinker and experience "let's see what happens ?" moments. This is how you learn, IMHO.
Node.js is indeed a great choice to start learning server side web development. No doubt about that. You don't have to learn Javascript first and then start learning node. Here you can find all the resources you may want. Also, have a look at this How do I get started with Node.js
Here is what I would recommend as your learning path. This is not even node.js 101. But, it will be a great start.
After completing this many tasks you will be good enough to decide what next you want to do.