That depends on the lens diameter. This is usually indicated on the lens. The filter holder is then attached to the lens with the appropriate adapter ring 

The size of the adapter ring depends on the size of the filter thread of the lens used. This is noted on the lens and in the lens cap. 

it fits in a 100 mm square filter mount, so it depends on the size of the mount adapter to the lens 

not 100% sure, but the filters of different brands usually have the same thickness, just minor difference, which could be ignored. 

All gradient filters, whether made of glass or plastic, are coated filters. As far as I know, there are no gradients in the glass. Is due to the production of glass. Nevertheless, there are good to very good results with the glass filters. Lee filters are usually made of plastic, with the ordinal number CR39, from which glasses are also made. They are also coated. In fact, they are very good. Due to this complex production, the filters cost a lot of money. And at Lee Filters they are not cheap especially, although they are made out of "plastic", except for the IR filters. They're made of glass. 

The od size is 100mm, the set comes with multiple different sizes to fit many different lens. You do not need long exposures for good moon detail, 500 sec at f8 works good on full moon 

Only one, because each filter comes with it’s own pouch and it will only take one filter. 

I have a 50mm prime, 24-70, 70-200 and a 35mm prime and it fits them all. If day as long ss your lens has internal filter threads and is one of the sizes listed you will be good to go. 

No, you need to thread the holder onto the lens itself. 

I use one on a Pentax 24-70mm filter size 82mm. Just make sure you buy the right size for your lens. I have the nd1000, and I am very happy with result. They also sell adaptor step down for your other lens.