1) Well like someone else commented on here recently I think this still mind is a necessary 'stage' but not the 'end goal'. In that Sheng Yen commentary to hsin hsin ming he talks about this stage specifically. That commentary talks about hua toa practice some, but a lot of it is about that sutra in the context of silent illumination style training. One of the main points was that you shouldnt try to cultivate this stillness. You just fully experience everything including thought wakefully and things settle on their own. Like you said Chinul might have known this though, and just knew what he was meaning when he wrote this and didn't elaborate.
3) If something seems like it would help I try to incorporate different things. After certain experiences I've had I've felt kind of stagnant if I don't practice, like I'm wasting my life or something. Some approaches don't really fit together. Also at a certain point I started to feel that I understood things intellectually, but that it wasn't really helping me that much. I try to mostly sit now. But sometimes I'll read stuff. That Sheng Yen hsin hsin ming commentary is very good. He rattles off common pitfalls I've fallen into before one sentence after another like they're no big deal. It's really kind of dense and I might be rereading that for awhile. Also I've started learning Qigong and it's improving my sitting posture already, helping with that shoulder pain I was having, making me breath more deeply. It's really kind of like moving meditation similar to kinhin. I should've started doing it sooner. There is a lot of woo woo type stuff on the internet about Qigong but once I found some good resources it started helping me really quickly. I tried some yoga stuff before but I like Qigong more I think.
So that's what I'm doing lately: sitting meditation, reading some short things to sort of keep that stuff in my mind somewhere, learning about Qigong, and coming here to see you guys talk or ask you all with questions if I'm wondering something.
5) Very aggressive way to encourage practice though isn't it? Aren't you a real man? Huh?
7) It's hard to say since I don't know much about korean zen at the time. Why did people think it was a bad time for zen in korea? I know there have been various persecutions against buddhism in China was that the case in Korea when they thought they shouldn't teach? I'm confused though, I looked up Chinul because I was unfamiliar with him and it said he received some kind of recognition (not dharma transmission) from Dahui?
It's really hard to say though. There are a lot of factors related to social environment, personality, or personal situations family wise or economically that could lead people to practice like that I'd think.