Hello.

Forum threads are sorted in a tree-like fashion (like on classic forums in the 90s, and a bit like that in the early 2000s).

Yes, a forum account and a hosting account are two different accounts; the email address is assigned to the hosting account (but only if you have a website, not just a dummy page). i mean yourlogin@w10.host

You can create as many accounts as you like, and they can have different quotas (I have about 10 accounts for different sites, and they are all registered to the same email address)