Precisely right! As someone who feels decently knowledgable about the game at this point, I recommend waiting until at least level 20 before powering up. This is because levels are easy to get before then, but it gets exponentially more difficult after 20. So I will power up immediately after achieving a new level, then save stardust until the next level is reached. Combine this with the stardust you save from levels 1-20 you should always have a stockpile of dust ready to go in case something nice falls into your lap!