Commenting so that I can see responses later. I have setup mesh for a friend in his rather large sized backyard, though I did it in a different manner. His barbecue is at the back of the backyard, adjacent to an outdoor power outlet, and the barbecue has a large cabinet below it. I simply stuck 6 foot outdoor extension cord inside that cupboard, and plugged in a powerline adapter and Asus router. Instant AiMesh with the powerline adapter as the wired backbone. It’s been working perfectly for over a year now.

The 68U is over a decade old now. You will definitely notice a performance increase with the AX-86U. For one, it doesn’t take almost 5 minutes to boot up. And yes you can still use the 68U as part of an AiMesh network.