I, or all other members here, use the same number for the same topic or related questions, as I used "1.1" for my reply to your question "1.1", whereas you used "2.1" for the same topic. This is the cause of the confusion so far, perhaps?
I didn't identify correctly what is a stem and what isn't.
This is a huge problem for your learning Japanese. If you can't grasp it, you will face many difficulties also in the future.
forms of verbs that can be used as a predicative (except imperative or volitional form)
書く, 書かない, 書いた, 書かなかった, 書ける, 書いている, 書かれる, 書かせる, 書かされる, 書きたい, 書きたがる, 書きやすい, 書きにくい or other combined verbs such like 書きすぎる, 書き終える or 書き出す, etc. etc. (including combinations such like 書かされたがっていなかった)
-masu stem of verbs/the form attached to the polite suffix ます (also know as 連用形, i-form, etc.)
書き (including potential 書け, passive 書かれ or other combined verbs)
forms of i-adjective that can be used as a predicative
寒い, 寒くない, 寒かった, 寒くなかった
stem of i-adjectives
寒 (non-conjugated part. い is removed from the dictionary form)
Note that the -tai form or -yasui/-nikui of verbs also perform as i-adjectives. Also, negative forms and ない are also treated as i-adjectives, but なさ, not just な, is used for そう as an exception, e.g. 書いていな
さそう or 寒くな
さそう)
na-adjectives
静かだ, 静かじゃない, 静かだった, 静かじゃなかった
stem of na-adjectives
静か (non-conjugated part)
As for 意味なんだ and わるいんだ, copula だ is attached to そう, therefore this そう is hearsay, as I already explained.
"Non-polite form of predicative (verb, adjective or copula, including negative, past, potential, -te iru form or other variations) + そう" is hearsay.
1.2) A)
してくれた is not passive. The subject of してくれた is 母, so the literal translation is "
stories my mother gave me a favor of telling to me /
stories my mother told to me".
B)
Actually, 子どものとき is a temporal adverbial phrase that modifies してくれた (Notice that "the time my mother told the stories to me" is "when I was a child", and it's not "stories when I was a child").
There is no strict rules where a comma should be put in Japanese, but it's often put after temporal adverbs such like 一年前, 昨日, 今度の日曜 or 来年.
の is needed if it's an attributive clause (子どものとき
の話).