1. "Why stacks of seven? Is there significance to this?"
Actually a lot of games use 7 pieces/cards/... to start out, it has probably to do with being an ideal number to make combinations, not too many, not too few.... also if you deal them in stacks of 7, the shuffle will be as random as possible. For this game 1 stack of 7 is too little so we play with 14. Probably you'll find a symbolic reference too in history if you are willing to search for it... (sorry not enough time for that today ;-) but my first guess is that it has a connection to the amount of days and the believe in several cultures that 7 is a lucky number)
2. "After each players turn, does he draw from the pool to replace the number of tiles he used in that turn? Or, does the game end when a player uses all his original 14 tiles and any others he has been forced to draw by the only 2 examples given."
Edit: No, you only take 1 tile out of the pool if you're unable to lay a "meld"... but you don't have to replace the number of played tiles (my original answer according to the way I used to play: You replace the number of tiles used after your turn until there are no more. )
3. "In other words, can the game end with tiles remaining in the pool?"
edited answer: yes. (original answer: No, unless you alter the rules a bit... for example you decide to play for 30minutes max. (or you follow another playing-way!))
4. "The instruction sheet that I have states that it is Original Rummikub Playing Rules ''The Sabra Way''. Is there another way and instructions that I am missing?"
Yes, there are many other ways, the 2 other most common ways are:
"the American way" Rules of Tile Games Rummikub
and the "International way" Rules of Tile Games Rummikub
And ofcourse there are plenty of different ways. Just set the rules when you start to play...