Part (1) is here.
I don't believe temperature is a big factor that can cause over-brewing. As previously explained, in a vessel with wide opening and small volume, a tea can rarely be over-brewed, even when very hot water is used.
Interestingly, in my observation, I've noticed temperature is often a big factor that causes under-brewing. In recent years, there seems a trend of recommending rather low temperature for green tea brewing. I believe brewing temperature can definitely be flexible, based on personal preferences and with other brewing parameters (infusion time, leaf/water ratio, etc.) adjusted. But I am a little concerned that more or less, lower brewing temperature is becoming a dogma. Many people are told they "should" use rather low temperature for green tea (and similarly, for white tea), and are worried that higher temperature would ruin a green tea. Traditionally, many Chinese green teas are brewed at nearly boiling temperature (205-212 F) , some high end green teas with a lot of young buds are brewed at a lower temperature of about 180-205 F), and very few high end teas (such as March harvest Bi Luo Chun and En Shi Yu Lu, the latter one similar to Gyokuro of Japan) use even lower temperature of about 170-180 F). Currently, a lot of brewing temperatures recommended by various sources are even lower than the lowest of above-mentioned brewing temperature. When brewing a Chinese green tea at rather low temperature, a potential risk is the tea can be under-brewed, and the drinker would find the tea rather "tasteless". So when a tea drinker finds a Chinese green tea (or a white tea) short of taste, the first thought coming up to my mind would be "try hotter water". It doesn't always solve the problem, but sometimes it does.
(This previous post includes some discussion about brewing temperature for white tea.)
I have been wondering what makes people think very low temperature should be used for green tea. I guess, the influence of Japanese tea drinking might be a factor. Many Japanese green teas require significantly lower brewing temperature than Chinese green tea. When some people extends their tea drinking from Japanese green to Chinese green, they may naturally think similar low temperature should be used. But in fact, most Japanese green and most Chinese green are significantly different and therefore require very different brewing methods. Another possible reason why people think low temperature is suitable for green tea is the thought of "the more tender the tea leaves are, the lower temperature should be used", which might be naturally intuitive, but is often untrue. Besides, some brewing suggestions are probably made for 16 oz. or larger teapots that are more commonly found in an average household. Then lower temperature is used to compensate for the steaming and volume effect as above analyzed.
Some green teas can be enjoyed with lower brewing temperature without being under-brewed. Usually this involves adjustment of other brewing parameters.
16 hours ago