1- Salary at QF is on a very strict scale, you cannot really negociate but you have to be careful that you have been put at the right level (i.e. that your diplomas/experience/job description, match the grade).
3- Yes QF is one of the best places to work for in Qatar, for sure.
4- No, although some companies do that QF does not. Still you will need an exit permit to leave the country.
5- Depends on the position, very hard to say since QF is a pretty "young" structure.
6-Depends on a lot of paremeters, are you a muslim, does is your wife willing to work, how old are the kids... And there are two french schools in doha, and they are good.