For the lowpoly it depends on how close you can get to the object. Normally these holes and the small gap won´t be part of the lowpoly geometry. A normalmap can be used for those details.
You have very high density, is that your lowpoly? or do you use turbosmooth? I keep my meshes as lowpoly as possible when doing highpoly so its easier and faster to change and not as much to mess upp. If its not your base mesh plz post it easier to see the edgeflow then.
You could just create a simple plane, add enough subdivisions to it and extrude the border edges down. Then you form a nice shape for the lowpoly and collapse the edges that you don´t need to hold shape.
if you run out of ideas try to model it in lowpoly first and then build up the needed harder edges of the subdivision cage from there on. I actually modeled this shape 3 years ago but its way to shitty to show :D