Unlike Illustrator, the path created by the trace bitmap does not need to be removed from a white background. The background is removed automatically when performing a single scan in the Trace Bitmap dialog.
Instead of layers, we'll just work with paths.
Inkscape doesn't let you set the path location to inside or outside. It is always centered. This means a few things need to be done differently
Select the path, and set it's fill to ffe384ff (this includes the opacity):
Duplicate the path (Ctrl-D) and set the stroke to ffd457ff, 10px, the fill to none, and the caps and joins to round. To get the inner stroke, select the filled path and duplicate it (CTRL-D), and shift click the thick stroke we just made. It should show "2 objects of type path" selected in the info dialog. Now do an Object->Clip->Set. This will clip the 10 px centered stroke to only show the 5 px on the inside:
To make the black outer stroke, select the filled path and duplicate it. Set the fill to none, and the stroke to black (000000FF) and 2 px, then send it to the botton (end) Again, to get a 1 px outer stroke, we set a 2 px stroke then send it behind the filled path with no stroke:
Making the large water outline is done the same way. Select the filled layer, and duplicate it, then set the fill to none and the stroke to A8C399FF, 14 px with a round cap and join. then set it to the botton (end):
For convenience these can all be grouped together, or alternately, just create a rectanfle below them, as set the fill the same as the land fill. (The eye-dropper tool is handy here).
Now save the image and export it at any resolution you want!