#5, there are tons of links which explain what Ukiyo means. The explanation on your link is correct since 'Floating world' is commonly used when people explain it in English. http://asianhistory.about.com/od/Asian_History_Terms_U_to_Z/g/What-Was-Ukiyo.htm
#9, It's not only used when people are flapping into a chair after hardly work. When they are sitting in a chair so long then, they have to stand up from the chair, they may say the word, yoisho. Or, many people use the word when they lift/push heavy stuff. Generally speaking, most of the time, it's used by aged people. Not so many young people use that word.
#11, it's not only for young people, but also middle aged people who don't have a job and are totally dependent on their parents for everything. In Japan, there are many Hikikomori, who are 40 or 50-somethings, and I don't think we can call them 'young'.
# 13, it's not actually 'Old school cool' since the meaning of old school cool is like that: http://onlineslangdictionary.com/meaning-definition-of/old-school
When people use the word, shibui, they don't mean it describes older tradition methods. It actually means sober, simple and quiet. For instance, sober coloured. There are other meanings for the word, shibui but this time, the writer just wants to inform that meaning only.
Then, the word, Shibui, it's not noun, it's an adjective.