Don’t have much to say or ask, but I too have built a Ardupilot Mower and an looking forward to being part of the club.
I also built a program like @Christopher_Milner that includes a perimeter and islands. One thing I do, since my mower is skid steer, is back up from first waypoint (WP0) at a 30 degree angle to the next waypoint (WP1), move forward to the next waypoint (WP1), and then reverse to Waypoint 2 (WP2). Doesn’t chew up the lawn so much.
Welcome to the group! I like the idea of going backward and forward. You can actually get the mower in to tight places by backing in and lining up along a fence for instance. With a big mower that has the center of rotation set between the rear wheels, it takes some space to ease over next to a fence close so you can drive along it. If you back in to get lined up, it is easier. It was a big discovery for me when I realized you can program these things to go forward and backward just as easy.