How long does an account have to be unused until it is inactive?
If an account is frozen, does that user's pet names become available right away?
It's definitely a year for an unused account to turn inactive.... I'm pretty sure frozen accounts clear after a year as well, but I'm not 100% certain on that one

A year for both, typically. Unless there's special circumstances on the frozen users' part, i.e. it was a self freeze and the user comes back after a couple months. (I did that back in 2013 for a couple months.) Mod-enforced freezes act the same as a ban.
Pretty much, yes. There's normally a given time and people who want the names will lurk about beforehand to snatch up the "good" names.
