Great Questions!
When deciding to get married, what does the ISTJ check-list look like? My checklist actually isn't long. I'm looking for a girl with a balanced'go get it' attitude, and isn't about all of the drama.
What could make them unsure of their potential mate? If what they say is good, but their actions don't match their words. Actions speak louder than words, and I think some girls have good intentions but overstate their abilities.
Will they ever be 100% confident in their choice of partner? (seems like Ne-inferior would get in the way, asking too many improbable 'what-if' questions) I don't think I will ever be 100% in my choice. and you are right, my Ne kills me sometimes, it takes any event and applies the worst case scenerio to it.
Does it take a long time to make your decision? Seeing as how you are the ultimate planner... For me it is. I tell people, relationships are hard, since you are dealing with a person. I've been to school, have a great career, and own a house. All of these accomplishments were easy, since they are pretty constant and predictable in most ways. But another person is harder, especially women, because most aren't objective, they are subjective, and their feelings can go on a roller-coaster ride where they don't even know what's going on. Since I have less control (not bad control; I just like working with experience (Si Si Si Si) I flip-flop alot.
I think as an ISTJ, you will know where you stand with us. That's one thing my girl can attest to. She's clear where I am and what my intentions are.