I am going to hire a third party security company for Penetration testing in our company network. I have already selected a pen testing and black box testing company to do them, but they have requested details regarding our network including; network setup, intranet, What data should be provided to them? and what data should not provided?
Given that the penetration testers have a limited amount of time (since you provide them with a limited amount of money) they can do a better job in that time the more information they have from start. Thus, if you are interested that they actually help you to increase your security you better give them all the details they want.
If instead you want to have a result which says that they did not find much in the time they had, then make their job as hard as possible and provide no information at all. But while such result might look good in a management report it will likely not reflect the true (in)security of your network.