Staking is a relatively new field. Tezos launched July 2018 and professional validators only started to appear with the launch of Cosmos early 2019 so there aren’t that many guidelines and educational resources available as the role and staking industry as a whole is still getting defined.
What are the ideal qualities (technical and psychological) that a new Node Manager must have?
I will let someone else respond to that as I’m no expert. I would assume anyone who has a solid understanding of the operating system you’ll be using, hardware and infrastructure (including building fail-safe systems), operational security, and of how the internet works. Several stakers I’ve met have taught themselves all of what they needed by asking experts and by searching the web.
What are the online courses or resources that I can share with him/her?
I’m not aware of any courses since every POS network is (slightly) different.
Do you know any blog or youtube channel teaching how to be a good node manager?
I’m not aware of any resources specifically for node managers since there are few people in the world who are full time professionals working on POS infrastructure, however here are a few more general resources that may be of interest: