On ISTj/ISTp, I think schroedinger's cat and Topaz put it well.

I think it can be simplistically summarized thus:

ISTj - rigid and inclined to impose rules on others
ISTp - flexible and unconcerned about what others do

In my professional life I often meet ISTjs as Quality Managers. In that job they're a nightmare because they make an already rigid and bureaucratic field even more rigid and bureaucratic. But in my present company the quality manager is an ISTp, and he introduces a refreshing flexibility to it. However, he also often does not do the job as thoroughly as an ISTj would.

As for XoX's type, I see signs of being a perceiver as Rocky said, and also of weak - so perhaps ISTp is really it?