Can you really get to 1800+ without opening memorization or do you have to be a chess genius like Michael de la Maza?
I haven't personally done it, but I'd say almost certainly yes (and the teachers and such that post on the internet seem to think so).
If you don't lose pieces to tactical shots, don't miss tactical opportunities, and know your endgames cold, you should have no problems beating sub-1800 players most of the time. But that's a lot to know/do.
Nah not really, working only on tactics won't get you a lot past the level that gives you free pieces, around 1500. In order to beat better players you have to have a good understanding of the position and a good gameplan, that usually comes from learning (learning! not memorizing) the openings as much as learning positional ideas.
About 1...e6 - I think it's a great opening for beginners, it's even what I played! You can even read the article I posted on this site when I was 1300 about the French opening:
http://www.chess.com/article/view/french-opening-advenced
When someone discovers a move that, when played, makes the player of the opening feel rather embarrassed at his position, that opening is refuted.
That's a refutation of a line, until someone finds a better response/previous moves for the other side, that's how openings evolve.
Talking about refutations the KID is in some problems lately
The only openings that are bad for beginners are bad openings and passive openings like 1...g6, 1...b6, etc.