What if I don't want to learn an instrument?

I'm interested in composition, not traditional performance. Is there a route to learning and making music without learning to play a physical, analog instrument?

Absolutely! The basic element is the same: you just need to figure out what part of the process you enjoy doing. The writing is one part, but there's also arranging, mixing, mastering, etc.

And it can help to have a basic understanding of an instrument but it's not specifically a requirement. For example you could download a software synth and start messing around with that. If you're sufficiently motivated, you could pick up an M-Audio USB keyboard for cheap.

And after finding the tool, is a teacher worthwhile or should I rely on self-teaching?

I had a classical guitar warm up guide which had an introduction by Robert Fripp. He included a short list of tips and one was that the value of finding a great teacher is that they can connect you to the culture of the instrument (I'm paraphrasing b/c I can't find any references). That's something that's difficult to replicate on your own.

That said, you can learn a lot on your own. There's no right or wrong approach so you should feel free to take the route you're most comfortable with.