I allready own a gt-ax600 and have 2 ac86u aimesh nodes. I will recieve 2 gt6 tonight (230 euro after cashback) to replace the ac86u's. I have use my nodes wired. Just to be sure best way to set up would be ax6000 as master and gt6 as nodes?
The GT-AX6000 as the main router will give you access to the faster processor (unknown importance in your use case), while one of the GT6s will give your network 2x 5GHz SSIDs with a wired backhaul.
As usual, test each configuration and see what actually works best for your environment, devices, and your expectations.