Great questions! I hope to answer them as correctly as possible. I'm not an EDH expert, and I'm certainly not the authority on applying Vintage skills to the format (I'm always hoping that some of the adepts, like Soly or Shay, would chime in more often).
I've been playing EDH for a little over a year, and the groups that I play in can be very competitive - to what some other players might consider douchy, and can be very infested by Islands (..Riku, ..Jhoira, ..Sharuum). It is for this reason that my
initial deck did not include many Wrath effects. Outside of Akroma's Vengeance, Austere Command, Decree of Pain, and possibly Sunblast Angel, boardwipes are dead against other blue decks in general, and combo decks specifically. This is the hardest part of the deck - finding the right mix of removal, card draw, counters, and situational answers.
Dromar does more work than Merieke, and is more specific to the deck's purpose than something like Sen Triplets. If you want to use something else, it's certainly not written in stone.
Consecrated Sphinx - this deck likes to draw cards. Sphinx is arguably the best way to do it!
Emeria Angel, Meloku and Platinum Angel, in addition to being really strong creatures, they all get around both Moat and Abyss.
Tidespout Tyrant is for the well-known infinite mana combo.
Twilight Shepherd is absolutely BUSTED. It was originally intended to thwart boardwipes (Jokulhaups, Obliterate), but can give you a x-for-1 with your own permanents. Also with Child of Alara, it makes people cry.
Akroma's Vengeance is the Balance of the format.
Brainstorm is just as amazing here as it is in Vintage. Other cantrips, however, are generally flimsy and can often get replaced with real card drawing.
Future Sight is part of another widely-played combo.
JTMS has been inconsistient. People will attack him more over any other planeswalker, so use him in conjunction with Moat, Akroma's Vengeance, or token makers.
Mystic Remora is good to set up right before a counter war.
Nihil Spellbomb and Tormod's Crypt are there specifically because of Reanimator-Child.
Thawing Glaciers - I can't say this enough. This is one of my favorite cards in the deck and the biggest improvement over the previous version. You can mulligan sooo aggressively if you have this, or a turn-one tutor in your hand!!
EDIT: ...Speaking of mulliganning aggressively, ideally, you want to keep a hand of land (obviously), one board wipe (remember that Moat and Abyss often count), one card drawer, or one tutor acting as one of these. Don't be afraid to go down to four cards or less if you have cards that will allow you to recover at some later point in time. You'll draw into counters and creatures reliably enough, as the game progresses. Ship late-game cards, like Eldrazi and Time Stretch, to the bottom of the deck. The rest of the game depends on your ability to identify what everyone else is playing, determining who's going to mess with you first, and knowing "Who's the Beatdown".
