I have mixed feelings about the rating of this box: on one hand, it’s easy if you have experience with AD, but if you don’t (like me)… boy, you’re in for a ride 
Overall a great learning experience, but there’s a specific (deliberate?) issue which made me lose a lot of time because openvpn wasn’t quite happy with what I did to my VM to overcome it.
All hints in this thread will set you on the right path so I won’t repeat them, but I have one more for root: keep an eye on the clock, even few minutes can make a big difference!