Since you'll be using Wilbur at some point during the editing process, you can smooth out the coastal areas and what not by applying an Exponent (Filters>>Mathematical>>Exponent) to your land masses. When I do that sort of thing, I tend to create a selection (Select>>From Terrain>>Height Range) so that I can isolate the land mass and experiment with the Exponent value. I also use a math function in the Calculate Height Field dialogue from time to time, but that's a bit more complicated. Fill basins will definitely create more flat areas, but I tend to shy away from that approach as it sometimes has a tendency to create too much flat area. Incise Flow, on the other hand, is more of a channel digging process that cuts elevation away based on the projected flow of water from higher areas to sea-level. If you're working through a2area's tutorial, he has a link to waldronate's tutorials for both Wilbur and FTPro, and I would strongly recommend reading through them to get a better feel for what they're capable of.

GW