One big thing you want to know

Look at this:

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It will be stressful for sure - from managing less than 10 people to over 20 people.
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Never try to manage that many people directly, that's just not wise, you're going to burn out yourself, and things will get into trouble again and again from time to time.

Anybody of this world should only try to manage at most 7 people -- a magic number. If you've got more people to handle, then delegate, split them into groups, and promote three or four people to manage the groups, and you only manage these group heads. Focus more on strategic things, look at the group heads see whether they do a good job, if not, change them -- you keep watching others to see who should be replaced.

Just in any case you don't have any formal textbook on leadership, use Chairman Mao's article "论党委会的工作方法":

书记甭管多大，直接管的就是一个班，是班长，把一个班带好，所管的人都去带一个班。想做大官没有不对，但要避免图的就是个热闹，结果成天草上飞。