Should I email old supervisor about my progress? I might collaborate with an old supervisor in the future and would like to keep in touch. Is it a good idea to send an email to him about the progress I've made in my career?  Also, what's the best way to approach this? I feel like emailing just to talk about myself is a bit narcissistic -- is it?
I just did that, and I often do. If I'm honest, I don't do that as much as I should. Anyway, unless told otherwise, which, imho, would be rare, that should be acceptable/desirable.

Of course, you won't just talk about your stuff, but ask about his/hers. You do have common interests after all. 

Professors are people too! There is no secret in talking to a fellow professional that you know. And, of course, never send a professor a lengthy message. 

Be polite, be direct, and informative...