I have the 77mm. It can't take a lens hood but you can fit a lens cap 

EOS-FX,You can use Canon EOS EF / EFS Lens on a Fujifilm FX Mount Camera body,, Your canon ef 75-300 1:4-5.6 is canon EF mount lens and fuji x-a3 is X mount camera body. so the adapter ring fit for your camera and lens. but pls notice, your lens is telephoto lens,we do suggest you could use one telephoto lens bracket that could be attached to the tripod to increase its stability. because the canon lens could not adjust aperture,so suing our adapter ring could not adjust aperture 

K&F have a list of which adapter will work for each lens to camera combination they support 

The filter only has a thread to screw it onto the lens, unfortunately it is not possible to screw a lens hood or another filter onto it. 49mm is the smallest size for the lens ... 

1. Install UV: Yes Install the magnetic attachment ring: Yes With magnetic attachment ring + CPL: Yes Only after installing ND1000: no 2. No need to be a bigger size"