Elo = your invisible rating. You start with, I believe, 1200 or so. You gain Elo when you win, and lose it when you lose. A new account gains and loses a lot of Elo per game so the system can quickly find their rating. If you make an 'upset' (You beat a team that had a higher Elo rating than you), you earn more, and they lose more.
Council = one of the 4 community 'colored' names on the forums. Adjudicators (blue) were just in beta before July 14th. I missed by less than a week
. Emissaries (green) are specifically tasked with helping the new player experience. They helped Riot write the tutorial, and wrote some other guides. They're very few in number and mostly idle right now; Riot will be retasking them soon. Council (yellow) have one or more of the following attributes: have a very very high Elo/are otherwise considered fantastic at the game, are or were part of an eSports backed team, run a league/other eSports function that's picking up LoL, or were invited by Riot/the Council. I'm not quite #1 quality, even back when I was top 200, but I hit #2 and #4. Wrenchmen (orange) are people who've spent a good deal of time helping out in the H&S forum. I'm one of these as well.
Keep in mind it's not just armor/MR, you also have to consider HP stacking (which, while more expensive, counters both types of damage). There is no one answer for armor magic resist, sorry. It's just silly to think you can reduce it to one or the other for even a general rule. It depends on your character, and your opponents.
There are currently no known 'hacks' for LoL. Bugs/exploits, there's one or two floating around. Are you somewhat exaggerating or are those numbers legit? 18 by 20 is pretty excessive. It is very possible to do a mixture of jungle and laning with certain chars, that is VERY potent. Basically, in between waves Trist rocket jumps her wraith camp, and picks up free gold/xp. It's very popular with certain champs. If he's grabbing runes, even more so. Other factors: they could've had someone getting them dragon (especially if she didn't help), towers, idk. There's a bunch of factors; I highly doubt it was a hack.
That being said, my eyes have bugged out a couple times too when the enemy solo just levels ungodly fast. I notice it most often with tryndamere when he combos solo mid with jungling.