1)When deciding to get married, what does the ISTJ check-list look like?
2)What could make them unsure of their potential mate?
3)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)
4)Does it take a long time to make your decision? Seeing as how you are the ultimate planner...
1) Marriage Checklist?

Probably something like this-
For her:
-Does she have a job?
-Is it a good paying job?
-Permanent or part time?
-Is she able to support herself?
-Is she good with money?
-Does she enjoy my activities/hobbies or at least hearing about them?
-How much debt does she have, if any?
-What is her family like?
-What is her background like?
-Religion?
-Is she mature enough and capable of being a good mother?

-Does she have a sweet/loving personality and is she attractive?

-Is she fun to be with?

-Could I see myself with her in the distant future?
For me:
-Do I have a job to support two people?
-Would my job be able to provide for her needs?

-Am I able to provide adequate safety and security for her at all times?
-Can I provide a home for both of us?
-Do I enjoy being with her?
-Does she understand my humor?
-Does she like my playful banter?

-Do I enjoy her activities or at least hearing about them?
-Am I able to be a good father?
-How much debt do I have?
-Do I appreciate her for who she is, not who I want her to be?
-Do we share the same values?
-Same religion?
-Do our families get along?

-Have I seen her through "all the seasons"?
-In other words, have I dated her for at least one full year and enjoyed it?
I could probably go on but it's a start....
2) Hmm... what would make me unsure?
Her background...
If she had a history of family issues, for instance, if she grew up in a broken home with substance abuse, instability, physical abuse, divorced/separated parents, and if she moved around a lot, that probably would worry me a little. It would especially worry me if she didn't have a good, stable father figure.
3) Will I ever be 100% sure of the person? Yes, I will.
4) A long time?

It depends, I would take a minimum of 1 full year (from when we first started dating) to make my decision, but probably not more than 2.
