About the subdomain and the multiple websites, sure:
If I’m not mistaken, you already have apache running, so the dns being setup, I would probably stop it, install discourse “as usually”, adjust the app.yml (ssl, socketed maybe) then setup an apache virtual host as explained by neounix and restart it
about Bluehost, you’ll probably need the vps or dedicated hosting, not the managed wordpress one, but beware
The easiest thing will probably be to create a digital ocean droplet and configure your DNS to point to it, NOT create a domain with whatever tool they have. I’d recommend first doing Discourse official Standard Installation before attempting to make it work with something else.