Coming from a timeline where pretty much everything changes from OTL, people have always been confusing for me. Unforseen events (i.e. assassinations and coup d'etats) simply perplex me; you simply can't predict them through research (unless you have a good lead). For unforseen events, you just have to look for solid leads in OTL and ATL history.
Another thing you are unable to predict is people born into ATL that don't exist in OTL. This also plays into unforseen events; for example, the leader of a fascist coup could be a person who just doesn't exist in OTL. As a result, I tend to avoid fictional people as much as possible, with the exception of monarchs born into ATL.
I would recommend to see what niche OTL people can fit in your timeline; all of my North American leaders in my timelilne are American or Canadian politicians in OTL. I had a discussion with SouthWriter on Marco Rubio and his role in the ATL nation of Florida once. Prior to that we discussed people such as Martin van Buren and the Roosevelts in that TL. Perhaps you might be able to find some info there.