I have not heard about hiking from Jinshanlin to Gubeikou. The road from Jinshanling to Gubeikou is very steep and dangerous and some parts are totally covered by wild grass. I do not recommend you do this.
Mutianyu is to the east of Jiankou while Huanghuacheng is to its west, so you can not go from Jiankou to Mutianyu then to Huanghuacheng, it will be a detour. Maybe you can go from Mutianyu to Jiankou then to Huanghuacheng or the way reverse. But the distance between Jiankou and huanghuacheng is too long, the hiking can take as long as 10 hours. Also, Jiankou itself is a very dangerous section. You need to have companions and must be very careful if you will go.