Hello,put on the CPL filter or mist filter then screw on the Variable ND on top.Stacking filters in general can create different effects and bring out your creativity. The only caution is that as you put more filters on the lens you can create vignetting or the cutting off of the corners of your picture. This can happen more with wide angle lenses. You’ll also get vignetting by stacking neutral density filters, depending upon which ones you stack and the order you stack them you’ll get varied effects. We don’t recommend stacking a VND filter but if you do, make it the last one because of the threads. 

Dear Customer, Thank you for your question. Please check the following steps to setting the focus: (Do not look at too close objects) Step 1. Cover the right objective lens with your hand or close your right eye, rotate the central independent focusing wheel until the image in the left eyepiece is sharp and clear. Step 2. Now cover the left objective lens or close your left eye, rotate the right eyepiece focusing wheel to adjust the diopter of the right eye until the captured image is sharp. 

Why not 

In principle yes 

Yes