Yes not restriction. You can sit for all exam. Bear in mind that sometimes exam time do clash. Although this was a thing of the pass, who know with monkeys on the job it could happen again. But that should not be your worry.

Yes, the booklet they sell is good enough. If you dont want to buy it then there is a better way. Read policies for all classes of insurance. If you can understand every provisio, then you will sure pass. If you see a loophole in any of the provision, then you are better off being an adjuster.

NO, you are free to do what you want. There is an expire date to the exam. You cant join an insurance firm after the expiry date of the exam. My infomation may be out dated. As I know it the exam is valid for 2 years.