I can update you from four years later, lol! I’m still self-hosting discourse but no longer using Varnish. Part of the reason is that I’ve moved discourse onto its own host and no longer need to reverse-proxy to it, and part of the reason is that in the end any performance benefits to having static assets served out of varnish’s ram cache were more than overbalanced by the complexity of managing varnish.
If that’s your goal, cloudflare’s free tier will likely get you what you want without any cost at all.