Tang Ho makes a clear explanation on the difference between 成/乘, but I would like to elaborate a bit more on the 2nd question.
Chinese people feel that odd numbers are “lucky numbers”, and tend to use them more when they assign numbers to certain cultural constructs. For example, Chinese emperors made their subjects build palaces with constant references ...
It is a reference/meme to an old Announcement in the Public Interest (a.k.a. Public Service Announcement) regarding television programme regulations.
(In a local diner)
(Sports commentator in the TV) 電視機：「即刻轉身射個三分波啊，又反超前一分喇！」
(For a brief moment, a basketball can be seen in the TV screen)
MTR just shot a three-pointer, told us to ask the government
"射三分波" is obviously a basketball term.
It is not a common term, but a great use of metaphor.
Imagine: The MTR spokesman was surrounded by reporters asking him tough questions, just like a basketball player surrounded by opposing team's guards who wouldn't let him break ...
To express “finish remaining work on hand” can use 收尾 in mandarin. And I think this is the word sounds closest to 手尾。So for 我執埋手尾就會走㗎啦, you can say 我做完收尾工作就走啦
唔好咁冇手尾 can be expressed as （做事）不要有头无尾
唔好要人跟(你)手尾 can be expressed as （做事）不要让别人帮你善后（or “擦屁股” ）
整傷脊椎骨就手尾長啦 probably has no similar expression.