The OP's first question was:
When one makes a bracha on food, does he make the bracha on a specific
piece of food that he needs to eat from?
See here for a relevant discussion. It is clear from there that the bracha goes on the specific food I am planning on eating. There is a machlokes regarding the rest of the food, as mentioned there.
We also see from Y....
I was only able to find a solutions to some issues you raised.
Answer based on the סידור רבינו הזקן עם ציונים והערות (picture below) and מאמר נוסח התפלה סי' יג:
Why do we say א-ל חי (nusach 3 and 5)?
See Shaeri Orah from רבינו יוסף גיקיטיליא who writes (printed in מאמר נוסח התפלה):
וכל הרוצה לבקש חיים טובים יתכוין למדת א"ל ח"י: Whoever wants to ...
I have found the מעשה נסים to the Hagadah who writes about why we don't make a bracha on the mitzva of recounting the Exodus of Egypt and includes a reason why there is no bracha on bircas hamazon:
ומה שנראה לתת טעם במה שלא תקנו ברכה כי עינינו הרואות שבכל דבר שתקנו ברכה בגוף המצות לא תקנו ברכה על צוותו העשיות המצות כי אינו בדין לתקן ברכה על ברכה דהא ברכת ...
This is actually a machokes rishonim, and machlokes haposkim [a dispute among the commentators]. The root of the question is: Do we say that when I make a bracha, it goes on all the food I am going to eat? Or does it really only go on the food I am holding and intending to eat first, and the rest of the food only is "dragged along" with the first ...
See this discussion regarding the blessing made on the mahn while in the desert.
Despite a discussion regarding the ending of the bracha, it seems clear from the sources cited that they started the bracha with the standard six words.
So a) and b) date back to the midbar.
I see a many reasons to be lenient:
In regards to brachos according to the Gra and Pri Megadim (and Bircas hamazon according to the Magen Avraham (see below)) the requirement of speaking in front of a king is described by tosfos 31b and shulchan aruch 185:4 (as understood by Magen Avraham) to mean that "even when he cannot speak in a truly appropriate ...
There are a number of answers brought down and several have already been listed. A few additional answers are as follows:
In Sefer Hamanhig (Hilchos Pesach, 64) by Rav Avraham ben Natan HaYarchi, he notes that Shehechiyanu by definition is only recited when the action being done elicits a degree of Hana'ah (benefit) such as with Pidyon Haben, Shofar, Lulav, ...