Are the images your income? It appears that you need more glass if you need to deliver a product with good resolution. Cropping a great deal might be more acceptable with the D800 but it is still no substitute for proper lenses for the task. Adding a TC will lower focusing speed which will get you further from your goal of faster, more accurate AF.
If, on the other hand, it is hobby, cropping will provide images for small web or print use.
Regarding your settings question: Raw, AF-C 9 point would be the mode I would use, with the center focus point relied on, VR off and high enough shutter for the action, at least 1/500 as a minimum so essentially the same you are using now. Stan St Petersburg Russia