回转 isn't used that often for making a U-turn, but you might still hear it sometimes. 回转，往回转, or 往回旋转 literally means rotate back/backwards. E.g. 把方向盘往回转.
掉头 or 调头 is common for making a U-turn. E.g. 师傅，前面掉头。
Don't know about China, but in Taiwan 回轉 mostly explicitly means u-turn performed by a vehicle. As for 掉頭, in addition to the literal "turn your head", you can use it whenever you are heading from A to B, then suddenly requires to return to A.
Example, when you are going to work by taxi, and your just found out you forget to bring something important, ...
回转 = "rotate" e.g. "1000rpm" means "rotate 1000 times per minute" = "每分鐘回转1000 次"
回转 (至相反方向) = "rotate to opposite direction" = "turn 180°/ turn around"
调头 = "turn around" (to the opposite direction)
掉头 = "turn one's head; turn around"
调头 and 掉头 are interchangeable when it means "turn around" But 掉头 can mean "turn one's head" in different ...
连朋友都没告诉过 = Had not told even his friends
即便(是)朋友也没有告诉过(他们) = Even though they (are) his friends, he had not told (them)
即便 means "even though" or "even if"
There's a verb "是" (being) in "是朋友" (being friends)
连他父母也不知道他是同性恋 = Even his parents don't know he is gay
即便(是他父母)也不知道他是同性恋 = Even though (they are his parent), ...
Continuing your example:
if we remove '已经'
still means 'not anymore' because of '现在'. The reason you say '现在' in this sentence must be to compare past and current, so '已经' is optional in this sentence.
Now if we also remove '现在'
Well, it still more or less means 'not anymore', because of the '了'. '了' here also somewhat ...
The answer to this question: What is the difference between 必须, 得, and 需要? already explained the difference between 需 and 須.
需(need) apply to noun. For example: "必需品" (品 is a noun)
須(need to; must) apply to verb. For example: "須知人言可畏" (知 is a verb)
必需品: necessity; essential thing
人言可畏 criticisms should be feared; gossip is a fearful thing
自习：practice by yourself.
When you said 自习, you more like describing the action, rather than the content. Also you still have teacher to teach you, but you just practice by yourself when no teacher around.(but you still have a teacher)
Or you can think in this way: When you study in school, there are several study section. teacher teach you, practice when ...
The Chinese Grammar Wiki article Simple "noun + adjective" sentences writes:
Nouns are linked to adjectives with 很 (hěn).
In cases when 很 is used to link a noun with an adjective, it does not mean "very", it's just a linking word: a dummy-linking adverb.
...in the case of these "Noun + Adj." sentences, you just have to think of this usage of 很 (hěn) ...