There is an outer coarse thread although I haven't tried stacking another filter. 

Dimming 7 f-stops 

The lens hood can be used as normal without changing the thread. Simply screw the filter on and then the Geli afterwards 

This camera is equipped with an 850nm infrared light, which emits a faint light at night, and most animals cannot be identified 

As K&F Concept ND2-ND400 filters adjusts the amount of light that can pass through with polarizing glass, a colour cast can't be avoided for all the variable ND filters on the market. However, K&F Concept variable ND filters are made by the best coating technology, which reduces the effect of the polarizing film on image color. *Based on our professional test, the colour cast of K&F Concept ND2-ND400 filters is around 290k while the industry standard is 500k.