That surprises me. I thought the current thinking was that content drive everything (and FAQs are certainly content!) and that having everything on one domain was better than subdomains. I’m no SEO expert, but I’d be interested to know the thinking here!
If you’re really going to run two ghost installs, you could probably set up some deploy scripts that copy header and footer files (and whatever else is common) between the two sites, but I’d ask your SEO expert for more explanation first!
The general and very simple rule is ‘if makes sense to use a subdomain because it’s clearly different from the top, it’s OK to use another’ (then security and technical stuff say thanks god!).
So we don’t want ghost.org/forum but forum.ghost.org and that applies with docs/kb/support, bots, apis, roadmap system.
Are tags different from the top domain? I don’t think so, so in that case it’s better to use ghost.org/tags/X