I would say red. It has the best common, the best trial, and is the aggressive color in one of the most aggressive formats ever. Starting out blue makes me nervous.
Mouth//Feed was the difference between my deck going 3-0 and 1-2 at FNM last night. 3/3 for 3 is a good speed bump and can really gum up the ground if you have a cartouche of strength to put on it (I had multiple games where the hippo got two of them). Feed always drew me 3+ cards and led to a game win when I was stable enough to resolve it.
I don't think it's crazy to take the green trial early if the rare was a do nothing like dispossess, black was probably a mistake even from someone who really likes the jund colored trials. To answer your question I would advise patience. At that point you don't even know if you will be in those colors at all and the white and red cartouches are just not splash material. The green trial is fine with zero cartouches if that's how the draft shakes out.
15 Amonkhet. Amonkhet has one of the most bomb dense rare slots I've ever seen and you'll be able to run even the double off-colored mana ones with Gift of Paradise. Trials are also fantastic, particularly the Jund colored ones, and with that many packs I would expect at least 3, plus all the cartouches you could ever want for bouncing and reusing them. In the event you whiff on a large number of rares Amonkhet is incredibly fast and you will probably have the option of just flattening everyone with r/x aggro.
I could see something like 15 SoI for Hinterland Logger beats or 10 AER + 5 KLD for u/r improvise working, but I would run pure Amonkhet.
The best dumb luck that I've had at a big box was foil Wooded Foothills out of a single KTK booster that I got on a whim (also found a $100 bill in the parking lot). My best clear box find was the Freyalise commander deck in one of those clear box with paper liner boxes (got Kruphix in one of the boosters).
The word "block" has a specific meaning in the context of Magic the Gathering that directly answers this question. A block is a group of consecutively released sets that are grouped together for the purpose of constructed play. They make up the pool of cards for "___ Block" constructed, simultaneously rotate out of standard and extended (while extended existed), and are generally drafted together.
Ice Age block was Ice Age, Homelands, and Alliances. Coldsnap was released a decade later. It revived the old Ice Age lore and mechanics, but that doesn't make it part of the block because none of the things that define a block apply to it and the Ice Age sets.
I'm running it in Maren of Clan Nel Toth and and it does work, but the mana investment is back breakingly high. I would not put in a deck without having a good reason, such as reliable recursion or heavy support for activated abilities (eg: Illusionist's Bracers and Training Grounds). On a scale of auto-include to unplayable garbage I would rate it as deck specific role player. The printing of Trophy Mage bumps up its value for blue decks.
Glimmer has a tough time competing in a world Mystic Confluence and Think Twice exist. Jace's Ingenuity has been largely pushed out of the format, but I would take it over Glimmer in a vacuum, since 1 more mana for 1 more card is more efficient. Unfortunately AER didn't do much to push energy into EDH, so Glimmer is just too far down the chain of medium cost draw spells to justify much play.
How useful would Metallic Mimic be (usually naming elemental) in the deck?
I wouldn't want it for the same reason I don't run anthems in general, it strands Marath on the battlefield. If you want to pump your token horde I would run something like Glory of Warfare, True Conviction or Shared Animosity instead.
The biggest thing Exarch has going for it is that it can tuck the gods, which are starting to become really problematic at my shop. I think it's more of a hidden gem than a top 50 card, but I do really like it.
Artifacts.
I could see something like 15 SoI for Hinterland Logger beats or 10 AER + 5 KLD for u/r improvise working, but I would run pure Amonkhet.
Ice Age block was Ice Age, Homelands, and Alliances. Coldsnap was released a decade later. It revived the old Ice Age lore and mechanics, but that doesn't make it part of the block because none of the things that define a block apply to it and the Ice Age sets.
I wouldn't want it for the same reason I don't run anthems in general, it strands Marath on the battlefield. If you want to pump your token horde I would run something like Glory of Warfare, True Conviction or Shared Animosity instead.