Yes
The spelling you are looking for is "vein" describing style or a distinctive element or maybe a line of thought or action. The word "vein" that you are looking for in your sentence is a noun. The word you used "vain" is an adjective meaning conceited, idle, empty, hollow, etc. and cannot be used as a noun or, from what I can see, in your sentence.
You spelled it correctly. HOWDY PARTNER
You pronounce it as the following:SuperCalaFragaListicsExPeeAleeedoshUsPS. That up there is not spelled correctly
Yes it is spelled correctly
You have spelled 'still' correctly.
Yes, engineer is spelled correctly in your question.
Flattest is spelled correctly. The others are spelled: silliest, biggest and sweetest.
Yes, surprisingly is spelled with an S. Surprisingly is how you spell it. You spelled it correctly.
You've spelled it correctly.
Convenience (easy access or availability) is correctly spelled.
It should be foreign.
yes, that is correct.