Not sure how many landmasses you should add exactly, but make it at least enough so that the fun of exploration won't be over too soon. Maybe seven more major pieces, with a number of smaller islands mixed in?
And yeah, the wonky polar regions sound good. Could be fun, I think.
And what about desert? Do we have any places that are really harsh and dry, with only a few oases to survive on? That, riddled with sand traps and quicksand pits could be good.
Not to mention, you could add some floating islands. And some natural land bridges (not like one piece of land connecting another, like an actual huge projection out of the water, similar to a root sticking up from the base of a tree, that arcs like a rainbow of earth, and it's huge enough to support a whole population). Even vanishing islands.
And let's not forget, something similar to the
Symplegades.
And maybe a cave in the middle of the ocean. Not an island with a cave, just a barren, lifeless protrusion. You can land on the edges of it, but about a couple hundred yards in, it just drops off into the landform equivalent of a drainage pipe. It may be a plain entrance into underground cave systems, or a natural aperture into some other world, or numerous other worlds, or even into all other worlds (connected with this story's mythos).
“…Judge not what a man has done, but judge what he could have done if he was a different bloke altogether. For art thou a leper? And a leper can changeth his spots…” --Rudy Wade, Misfits (Series 4, Episode 8)