This is a cool idea indeed!
Love the short links idea. Have you considered using QR codes instead? if this is a print book then QR codes can also be a quick way to get to the related topic on your Discourse.
Note that Discourse supports short links to topics, e.g. https://meta.discourse.org/t/-/01 would link to the welcome topic for this forum. ff7.com/t/-/01 might be a little too clunky for you. So a redirect really seems to be the way to go.
Another consideration is that Discourse prefers to be on a subdomain not at the TLD. It’s possible to do it at TLD but takes some extra hackery. Maybe you want to install a URL shortener on ff7.com - there are lots of open source options for that.