Try: just using a premade script for a while, and every time a character does an ability does something you don't want it to, take a look in the AI script, find out what's making that ability happen, and tweak it somehow.
If you're just trying to completely script out your character at once, I would get overwhelmed a lot and I program as my day job. It's also impossible to really predict what will end up being useful.
Also, like @crdvis16says, you don't have to automate everything, just the important stuff. There's a lot of abilities in the AI scripts, but most of them won't ever be relevant; the AI script just starts with the top ability, and if it's not there, moves on to the next. So there's tons of abilities because they wanted to the AI scripts to be useful for most players, and so they stuffed tons of abilities in there for a narrow set of triggers. A more typical AI script for me is just one that checks to see if the character has a perception inspiration, and if not, uses Tactical Barrage, with a 10s cooldown. One ability controlled by a comprehensible use case.