Hello - I use the adapter to adapt a non AI lens to my Sony with another adapter (Canon to e-mount) - this way the focus works on infinity. I hope that answers your question. 

I always prefer to buy filters for my wider lens and then use step ups. Quick tip: if you’re using an wide angle lens like 20mm and less I advise you to use always a filter wider then your lens to avoid vignetting. My wider lens is 77mm so I always buy filter of 82mm. I hope it helps you. Peace! 

Yes. I use this with Nikon bellows and with Non-AI lenses. There might be isolated exceptions (exotic lenses). And, by the way, I think this is an excellent product, well made, precise, good item. 

Firstly, let's talk whether you need Nikon AI adapter ring or Nikon G adapter ring.
If your lens mount is AI, please choose AI one, if it is G please choose G one, there difference between them is G adapter ring with a aperture control ring.
If you want to use Nikon AI lens on this Nikon(G) adapter ring, it could be attached, but the aperture control ring could not be used，as there is a pin on Nikon G lens that could move the aperture control ring but no on AI lens.
So why have a separate adapter for the lenses with the 'G' designation? While the G lenses are the still the same physical F mount, the G indicator means there is no aperture dial on the lens itself. So while the G lenses will physically fit the standard F mount cameras and adapters, there is no way at all to change the f-stop on the lens. The adapters marked as Nikon G Mount are specifically made for those lenses in mind and have a dial built into them that allows you to control the lens iris from the adapter!
so here let's discuss the 4 items
KF06.068 AI mount, aluminum material
KF06.286 AI mount, with 1/4 Female thread screw for mounting onto the tripod
KF06.309 Ai mount, cooper material
KF06.070 G mount, aluminum material
 

It will work with all nikon lenses. The ai-s and D lenses are easiest as you can set the adapter to the largest aperature and then use the aperature ring on the lens to fine tune. With the G lensyou have rudimentary control over aperature with the adapter. Think there are only 4 or 5 settings on the adapter.