amfoto1 Loc: San Jose, Calif. USA

Your 50mm, 70-300mm and 50-500mm lenses are all "full frame capable" and will work fine on a D750.

While you can fit the other lenses to the camera, it will either shoot in "cropped, DX" mode where it only uses part of the sensor or the images will show strong vignetting and have to be cropped in post-processing. The end result is the same, either way... the images are cropped.

The 18-200mm and 12-24mm lenses are "crop" design lenses. They aren't designed to make an image circle large enough to cover the larger "full frame" sensor in the D750.

Even though the 60mm macro also a crop design, it's actually fully usable on a full frame camera. It doesn't show any vignetting I can see. (Note: Another possible concern is that some "crop" lenses use a retro-focusing design that causes their rear element to actually protrude into the camera to an extent, which might physically interfere with the mirror in a full frame camera. This is not a concern with the Tamron 60mm because it's an internal focusing design.... it doesn't change length at all, front or rear, when focused closer.)

After the cropping (which will vary to some extent with zooms), you'll basically be left with approx. 10MP images instead of the 24MP the D750 is capable of shooting. That's a major reduction in resolution even compared to your 16MP D7000. So while you'd potentially see some improvement with three or four of your current lenses (the FX lenses and the Tamron 60mm).... You really should plan and budget to replace the other two DX lenses in order to get your money's worth out of the FX camera. Equivalent FX lenses also will necessarily be larger and heavier. (Note: The Tokina 12-24mm covers FX pretty well at the 18-24mm end of the zoom range... but vignettes heavily at the other extreme. I don't have and can't test the 18-200mm lens, but it's pretty safe to assume it will crop heavily at most focal lengths and especially at 18mm end of the range.)

You make no mention of WHY you want the D750... You don't say what you think you're missing with the D7000, that you are hoping the FX camera will provide. You also don't give us any idea what you shoot or want to be able to shoot that you can't now. This info would be helpful, for better feedback to help with your decision. FX cameras are a good choice for some things... but DX cameras can be a better choice for other stuff. You could keep the D7000 and use it alongside a D750, but might be better served upgrading to a newer DX camera like D7200 (24MP) or D7500 (21MP).... It's pretty hard for us to make recommendations because we don't know what you shoot or how you use your images.

MauiMoto Loc: Hawaii

The 50mm and 70-300mm you mentioned are both full frame and perform excellent on the D750. The 50 is pretty wide on full frame, I would add a 35mm f1.8g fx if you want wider.
This was taken at 35mm with D750.

(Download)

Dr.Nikon Loc: Honolulu Hawaii

Excellent MM