I killed Irenicus and my soul dragged me to hell or something. Then I killed the old antagonist Sarevok. Then some demons made me make choices. And there's this big ole' file called final save in the savegame list. Is this when I should start clicking on the Throne of Bhaal icon when running the game?

Did you have the final battle and cutscene yet? When you get to a forestish area with stone heads littered about, you're in ToB.

It sounds like you've probably accumulated all the tears of bhaal if you met up with S and solved all the tasks posed by the demons. If you haven't battled Irenicus yet again, then no, you're not done yet. I think you need to explore the area and figure out what to do with the tears you've accumulated.

As Sir G points out, there will be a fairly definitive cutscene revealing the fate of Irenicus, a final wrap up in Suldanessellar, and then you'll materialize in a forested area that will mark the beginning of TOB. Good luck!

no, you're not up to ToB yet. You need to finish the area you are in first.

Great. Thank you. I have the tears of Bhaal but I haven't fought Irenicus yet.

once you complete the fight, the transition to ToB will be made automatically as long as you have already installed ToB.

Good hunting!