I'll also say that having a definitive ending point is a really good idea. Also, the further back your POD, the more difficult things are. I tried to do a "Carthage Victorious" TL back on AHDC once. And in the beginning, it was a relatively easy thing to do. But eventually, you get to the point wherein your not writing Alternate History but pure Speculative Fiction. For example, Hannibal leveraging his military victory into a political career is a plausible enough thing. Hell, you can get some idea of how said career would go, because he took political office in Carthage after he lost. But if you try and extrapolate what an independent Carthaginian state would look like in say, 0CE, it'll be tricky.