Stimulant is crafted in the Mortar & Pestle. To make Stimulant you need to put 2 Sparkpowder and 5 Stimberries into the Mortar & Pestle and click craft. For bulk crafting, just remember that you can always use more than one Mortar & Pestle. Simply load up a few and start crafting in each.
Now as far as bulk harvesting of the resources required for such production goes, there are things that can be done to make life easier here too. Check out these two pages, where I cover both harvesting and bulk harvesting of these resources.