1 昨天他不来，今天他再不来，我们去找他吧。 这个句子是最恰当的。“再” 表示“will happen again, has not happened"，比如：”我要再去一次北京“, which mean I will go to Beijing again. So here "不来" has not happened, if it happen again today, we go to find him. 2 ”还“ is more causal, and if you say "昨天他没来，今天他还不来” that means he is still not come today, it is already know the result is "not coming". So if fit your sentence, should be"昨天他没来，今天他要是还不来，我们就去找他“，here ”要是....就“ is same to "如果....就”，which is also more causal. 3 也/还 They can both mean happen again, and "还“ will more emphasis "still". And the thing has already happened. So if you say "昨天他没来，今天也不会来" means he will not come today,too, so it has no "if" meaning in it. And "昨天他没来，今天还是不会来" will be more natural, and emphasis "still will not", also mean he will not come today. So "也/还不会” is not fit your sentence.

我爸给我买了一部新车。

When you praise, use "太 adj 了”, when you describe, use "可 adj 了“ ex. （you are eating something...)这个真好吃，太棒了！ (later you tell your friend this is good) 我吃过这个，可好吃了！/可棒了！

In fact, there do have a subject "我” but omit. Because when we say “记得” we most of the time means "I remember...", we can't enter others memory, if you want to say somebody else remember something, then you must give the clear subject. And when you omit the subject 我，the whole sentence will have a mood of recall, sometimes full of emotion. So the translation should be: " I remember that my mom alway bought me wheat cake when I was a child." And you can look the sentence structure as : 记得+time+svo（a sentence）, in Chinese sentence order, "time" will before verb or sentence. example: 记得昨天他和我说过这件事。-----I remember he told me this thing yesterday. And the "time" can also be "when something happen" example: 记得第一次看到你的时候，你穿着红衣服。

if it is because of hungry, then "我饿得肚子咕咕叫了“ And one of my friend told me that "stomach" in English not just one organ which match ”胃“, so if it is not for hungry, but for some reason uncomfort in venter, 我的肚子咕噜咕噜响/叫。

我从来没有头皮屑。 never 从来没有

平常口语中可以说”内行人” “内行”，可以说“我是内行人”，“这方面我是内行”。“他很内行” “行家里手” is a little formal.