I read a piece once from someone on the theme of "things I know, but that no one else seems to". Briefly, here's one from me:
Nobody wants to work on infrastructure. This means that if you get an infusion of cash that leaves you with a source of funding for your project, and if you have any aspirations at all of attracting a community of volunteers—that is, people who will put in work to help out, despite having no obligation to you or your project—then the absolute first thing you should start throwing money at is making sure all the boring stuff that on one wants to work on is taken care of.*
Not realizing that you need to remove the roadblocks that prevent you from scaling up the number of unpaid contributors and contributions is like finding a genie and not checking to see if your first wish could be for more wishes.
This is a topic that would benefit from case studies. Examples (of projects that get this wrong) aren't scarce, but I'll save that writeup for another time.
*Note that "boring stuff" includes not just building and keeping things running, but also the boring job of continuously casting a critical eye at the contribution process itself to figure out what those things even are.