I just got into this game a few months ago and after playing some aggressive catch-up and almost having every available Pack the game currently has out, I'm wondering when we find out about upcoming Heroes in the announced Packs. I see on the FFG site that there are three Packs coming for use with The Lost Realm but they only hint at possible Card types. Is it just a speculation game until the Packs actually release or is this information available somewhere?

It doesn't matter to me if Sam's old Gaffer is the next hero coming, I'll still be buying the Packs due to being hopelessly addicted to my favourite Tabletop hobby.

Usually unless they spoil it in the article, you won't find out until closer to the packs release date. There's some exceptions (the new Merry was spoiled without ever being mentioned in an article), and checking on places like Cardboard of the Rings Facebook page or reading posts here usually keep you in the loop pretty well. To answer your question though: there isn't a place where every packs hero is confirmed for the upcoming cycle.

We only know what is spoiled in the articles, and whatever news we get usually generates quite a bit of discussion here. Erestor from AP4 was revealed today, for instance! But all we know about the heroes in AP 2 and 3 are their spheres.