You can also try Lensmaster for a gimbal, there have been many favourable mentions on UHH, I use one and have no complaints. Although sold in the U.K. They do deliver to the USA.
I use peak design slide straps which are comfortable and easy to remove if i wanted to add a wrist strap. However i find that the peak design wrist strap not very workable for me as it restricts movement of certain fingers, so try before you buy.
I had the D70 then D90 and D7100 but now use a D750, but I mostly bought FF lens as that was my destination. If you only have DX lenses the look at the D7100, D7200 or D500.
I use a D750 for action shots and set the auto ISO maximum to 3200 and minimum shutter speed based on lens chosen. If noise is ok I use capture one but if noise is more obvious I use DxO to process RAW images.
As a previous responder says why not think about the 70-200 f/4, its my go to lens for action shots. Its cheaper than the 2.8 and lighter and easier to carry all day if required. I think I read on DxOmark that is as sharp of sharper than the 2.8.
I also use an iPad Pro on the road and an external hard disc to store my images. My software is capture one or DxO depending on circumstances. As I do a lot of batch processing of action pics for uploading to a sports website I need to be as fast as possible and capture one allows me to do that quickly. At home I transfer the images from the external hard disc to my iMac.
I have the tokina 100 and use it for both macro and other outdoor uses and find it a fine prime lens. I think anything shorter than 100 will not be as useful.
I shoot amateur sports using RAW and convert them on a batch basis to jpg. I also apply other editing adjustments on a batch basis to the RAW images so not requiring all photos to be adjusted individually as stated above. I do scan the batches for anomalies that might require individual or smaller batch adjustments.