I'm just going to add on to this with a tip, considering it makes potions go so much faster, which makes for more time to use the potions!
If you do four of the first-level things, when they combine, you'll get two second-level ingredients. If you combine five first-level, that makes three second-level ingredients. Which immediately makes a third-level ingredient.
Combos are awesome, once you learn how to make them happen.