They’re just being responsible. There’s a chance that incorrect practice will cause imbalance and you will have no-one there to help. Imbalance in most ways will sort itself out with rest, sleep and healthy lifestyle, but in some cases, especially if there is already imbalance, it can get difficult. Imagine you started qigong with a heart condition, brought in too much yang energy into your heat and gave yourself a heart attack.
You can mitigate this by being slow and careful, and taking care of any discomfort by dialing it back and grounding, the go for a walk in nature and calm it down.
Tip: if you go red in the face, start feeling stressed and your heart starts beatng hard, you get palpitations or your breathing becomes difficult, do that ^ stop and ground and bring yourself back to baseline.
Having said that I’ve never seen anyone having issues, unlike kundalini practice where lots of people report issues, qigong is considered safer than kundalini meditations for this reason.
Personally, I think this is WAY safer than say “vampirism” or out of context “third eye meditations”, which also get reports of issues, sickness and headaches.
No, you will pick up these skills by practicing the microcosmic orbit.
Any point. Your book is silly, I already told you this and gave you better ones.