Good topic, Jan! Good for Ranger in providing tips about its inks & what fabrics work 'best'. When in doubt; try it their way, eh?

Heat setting? See above. When I taught fabric painting/stamping with craft paints, I would share my experience with students. Sometimes I heat set & sometimes I don't.
Another important factor is laundering stamped fabrics. I always recommended gentle detergent & cool water. If the item could be turned inside out (tee/sweat shirts), I do. If using a dryer, keep the temp lower than 'inferno'. Heat often breaks down inks & paints.