I'm late to the game but....
Currently (unless I'm missing it) I don't think one can define the wall thickness before the infill mesh starts, except for the top and bottom of the model.
For functional engineering models, the wall thickness parameter is pretty important to have, so that the part can be modified after printing (thread tapping, heavy sanding, mill/turning critical dimensions etc) and for strength/stiffness reasons.
Such a parameter is standard in most other slicers slicers (Slic3r calls it "Perimeters", Cura calls it "Shell thickness", MakerBot calls it something else I can't remember)
+1 the requests for a true 100% solid fill, it should be available for special case parts.
+1 Julias recommendation for transparency of supports
Cross sectional / slice view. Most packages have this.