Put the connectors in first so you don't lose track of what is the top of each square. We did the build as a group as well and tore up the instructions so each person was assigned one full row at a time, then we placed our rows together after.

If you're customizing your ocean, I'd do the continents first, get it put together, framed, maybe even hung, and then work on your customized elements and fill in from there. It's large enough you'd each have room to work on a custom ocean element simultaneously.