kaydi

I think, these are idiomatic and contextual matters that depend upon your conception of the nature of God, i.e., the conception decides the appropriate words for the translation, etc.

However, what you should be asking is that why کُنۡ فَیَکُوۡنُ in the ayah you quoted occurs as کُنۡ فَیَکُوۡنُ whereas it unanimous in grammar that jawab amr is majzum so why is fa-yakoon not fa-yakun?

 

Surah Yusuf, verse 28:

فَلَمَّا رَاٰ قَمِیۡصَہٗ قُدَّ مِنۡ دُبُرٍ قَالَ اِنَّہٗ مِنۡ کَیۡدِکُنَّ ؕ اِنَّ کَیۡدَکُنَّ عَظِیۡمٌ

Then when Aziz saw his shirt torn from behind, he said
'no doubt, this is the device of you women. no doubt your device is great'.​

Yusuf Ali translates kayd as 'snare'.

 

what is the most befitting translation for this word, which occurs, among other places, in sura al-Qalam, verse 45:

وَ اُمْلِیْ لَہُمْ ؕ اِنَّ کَیۡدِیۡ مَتِیۡنٌ

And I shall grant them respite, verily, My secret planning is very strong.
​

From http://thesaurus.com/browse/plan

Here are some likely translations:

My arrangement
My method
My policy
My procedure
My strategy
My system
My stratagem
My design
My organization

I feel that the word 'plan' has connotations of 'thinking', 'deliberating' and 'pondering' which are flaws in respect to The Almighty, The All-Knowing Creator:

بَدِیۡعُ السَّمٰوٰتِ وَالۡاَرْضِؕ وَ اِذَا قَضٰۤی اَمْرًا فَاِنَّمَا یَقُوۡلُ لَہٗ کُنۡ فَیَکُوۡنُ​

JazakAllah.

Wassalaam.