Yes, for an entire position. Not sure I understand you, but the P&L at expiry is simply the above with the final spot price.
Just that the P/L at expiry can be calculated a priori with no Greeks. It's simply a function of the intrinsic value of the position (i.e. a function of spot and strike prices).
Yes true, and the result from calculating it that way, should be the same as the result from using the above formula, with the final spot price inserted.
This is a great exposition on time factor of trading options or any other assets. Great words, Thanks