It can be used both in restaurants or guests (uncommon guests or elders) at home to show courtesy. However, using it on close friends/relationships might sound a bit weird, in which case, you might want to use 快吃吧/开动吧 (Let's eat).

v了v refers to the action lasted a short time or the action happens for just once. 笑了笑 then means to smile for a little while (not to keep smiling). also, 挠了挠头 means to scratch his head for a bit. Usually, v了v is used together with another action, either as a predecessor or a successor , it rarely forms a sentence by its own.

Both are correct, based on the context. However, if you want to emphasize on "finish", use 光 instead of 完。 啤酒已经喝光了。Meaning beer has been finished up, no more left. The same rule, 吃光 (to eat up)，用光 (to spend up)，卖光 (sold out), etc.

1) If you want to describe TV news (新闻）, you may use 晨间新闻（早间新闻） or 晚间新闻。Because 新闻 is a bi-syllabic word, so it's preferred to use a bi-syllabic to pair with. However, if you say 早新闻/晚新闻 is also fine, but never 晨新闻 as it sounds weird. 2) No difference. Just two styles of translation. Meaning ice cream.

Hi, my suggestion is that 被 cannot be used in every situations that has passive meaning. In Chinese, 被 is usually used to describe negative results, or results that you don't desire. For example, 小王的自行车被偷了。他被他爸爸打了一顿。我的咖啡被他喝光了。 事-解决；书-还给张经理；会议-举行 are quite neutral, not negative at all. So we'd avoid using 被 here. Alternatively, you may say: 这件事儿解决了 我同事把书还给了张经理 李先生 主持(host) 了今天的会议。 举行 is for large events, like annual meeting, sport games, election, etc.

洋葱3个，切成圈。苹果2个，切块。辣椒1只，对半切开，去籽切块。

Only when a verb is VO compound. 签(V)名(O)，留(V)言(O)，then you can use V了O to indicate the V actualized in the past, like the past tense. 收到 and 忘记 are not VO, therefore you should plus 了 at the end to indicate past tense.