I am living 200 km away from Majmah...its on Riyadh Highway...a road side large town of 130,000 population..i have seen your questions, i am here since 5 years and almost know completely this area.
Ans. to Ques. 1: Salary seems little less than the normal, but they are writing special allowance 30-80%, so they can accomodate the deficiency in that, working with GOVT sector of Saudi Arabia is v.v.safe and facilitating.
Ans. to Ques. 2: In Saudi Arabia, when you are coming on proper work visa, then DO NOT worry about health / medical insurance, your Employer will be completely responsible for that, not much room for negotiation will be available, what they have decided, they will offer you, or they will increase their offer on basis of your experience only.
Ans. to Ques. 3: SAR 15000 is good enough for a family, you will live luxurious life and will spend 5000 here in saudi arabia, your home, your commercial bills will be free (i m sure, paid by Employer), medical free, transportation free, so you can save an average of 10,000 per month out of 15,000, as the living cost is much affoardable here.
Ans. to Ques. 4: No problem, you can get a job even in the same university where your husband will work, or in annnnyyy other organization, its not prohibited, though on your IQAMA ( residence permit) it will be mentioned that you are not permitted to work: but your new employer will get you a work permit, so no problem, if you are qualified, then you can get and take work.