1) Kind of, maybe. If someone filled out an RBC application, there's a sort of assessment on that, but it's pretty boring. "Does he accept counsel well? Describe his spiritual qualifications. Etc." Maybe there would be a brief assessment of sorts on persons nominated as elders or MS on the CO reports.
There will be a file with "move in" and "move out" letters. Any time someone moves into or out of the congregation, a letter is sent describing, (yeah, assessing) the family. Maybe ~80% of those are pretty bland ("Joe is a regular publisher and is enrolled in the Theocratic Ministry School. His wife Suzy is a regular pioneer and..."). About ~20% are for "problem" cases and go into more detail about stuff they may have been counseled on, judicial restrictions, problems, etc.
For the average rank & file who don't change congregations there are no "assessments".
2) Not likely, unless the complaint led to some sort of judical action
3) Very unlikely. Well, on 2nd thought, if there were cases of child molestation in the congregation, there may be something in there that the WTBS wouldn't want known by others.
4) Absolutely, in full gory detail - names, places, dates, etc. The files are theoretically in sealed envelopes, so if you tamper with them they'd know someone had done so.
5) Not sure what you are after - the WTBS does a pretty good job of embarrassing itself
6) Congregation files are supposed to be kept at the Kingdom Hall in a locked filing cabinet, and only elders have keys.