#1- yes. Prusa silcer and slic3r in the print settings>advanced select solid infill every XXX layers. You'll have to calculate the number of layers based on desired spacing and layer thickness.
#2- yes, but fiddly. You can insert modifiers and change wall thickness at each section, so the bottom will have thickest walls, and then set the wall thickness to smaller values as you go up in Z.
Ultra MegaMax Dominator 3D printer: [
drmrehorst.blogspot.com]