Those are indeed some promising shapes. What era are these people waiting for a home? I could see that temperate/ subtropical convergence of isthmuses and inlets as a rich ground for commerce, conflict, migration, and (based on your thoughts about this being a supercontinent actively agglomerating and/or splitting) geological interest. The major bays of differing amount of protectedness gives reason for different groups to develop differing sailing methods, maybe close enough overland to have some interchange.

What are you thinking about overall climate -- major polar ice, scant ice caps, or none?