You've been given a lot of good and sometimes confusing information here. It boils down to this, get what you like, want and can afford. It doesn't matter why you want FF if you can afford it and want it. I prefer FF myself but I started shooting with Nikon film cameras.

If money is no object then as has been said before, the Nikon D850 is the current favorite. It has all the bells and whistles - - fast auto focus, great ISO range for low light with low noise and many more features. On the crop sensor, DX, side is the D500 which is the top of the line Nikon DX camera.

If you want a full featured camera without spending the money for the D850, then the D750 with Nikon's 24-120mm kit lens would be my choice. It gives you many features of the more expensive cameras but at a bit more reasonable price. It is a FF, FX, camera with great ISO settings for low light photography with low noise. It is a great camera for sports and the other areas in which you are interested. It is a very flexible camera and allows you to make many menu adjustments to personalize the camera for your use. The D750, D8XX, and D850 all give you the option of shooting in fully automatic mode, fully manual mode and a number of in between modes like shutter or aperture priority and more.

The 24-120mm is a great general purpose lens that will serve you well as a starting point. In time you will probably want some more specialized lenses but this is a great lens to start with.

A refurbished Nikon from Nikon, B&H Camera, Adorama and a few others would be a great deal. Watch the Nikon site and occasionally they offer a 10% discount on their refurbished gear.

Regardless of which camera you buy, if you buy Nikon, get Steve Perry's e-book on the Nikon AutoFocus System.

Good luck with whatever you choose. We all have our favorites and sometimes it is just because that is what we like. I love my D750. ☺️

How about a picture?

I love my D750. Some good advice was given above. If you have very many DX lenses that might be a compelling reason to stick with the DX format unless another reason is driving you to the FX format. I chose FX because it matched my Nikon film cameras and I didn't have to think about what a 24mm or a 50mm or whatever lens would do. I already knew without having to think about it. I also liked being able to crop and still have an image that I could print. You probably know that FX lenses are more expensive than DX lenses. As for the camera, I love it's low light abilities. I love taking night shots or indoor shots with low light where flash isn't allowed. I get great shots at high ISO with very little or acceptable noise. I like that I can shoot jpeg and RAW at the same time and save one to memory card 1 and the other to memory card 2. I love the flexibility of this camera and how the menu let's me set this camera up to suit MY needs and preferences.

Wharever Nikon you choose, be sure to get Steve Perry's ebook on the Nikon AutoFocus System. In addition to explaining the system he gives lots of tips on configuring your camera so that it works best for you.

Good luck with whatever you choose.

Here are a couple of mine from Hawaii.

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