Need:
$ Thousand-Year Storm
Murmuring Mystic
$$ Ral, Izzet Viceroy
$$ Reiterate
$$ Isochron Scepter
$$$ Paradox Engine

Consider:
Dark Ritual / Cabal Ritual - Spell-based ramp to jump ahead early and to use for a big turn late
* Pull from Tomorrow
* Kolaghan's Command
* Bonus Round
* Mizzix's Mastery - Cast more spells!
Dimir Locket
Decree of Pain - More boardwipes
Cruel Ultimatum
Increasing Ambition - Synergy with Kess
Epic Experiment - Stormy card
Gamble
Negate, Arcane Denial, Remand, Pyroblast, Dispel - Good counters
Melek, Izzet Paragon - Cast more spells!
Comet Storm
Dualcaster Mage
Snap
Forbidden Alchemy
Ancient Excavation
Cut // Ribbons
High Tide
The Mirari Conjecture
Mystic Remora / Rhystic Study
Burning Vengeance/Secrets of the Dead - Payoff for casting from graveyard
Dig Through Time - Very good, but don't really want to exile my graveyard
Rakdos Charm(!), Go for the Throat, Reality Shift, Crosis's Charm, Comet Storm, Silumgar's Command - Decent cards from the pre-con
Sleight of Hand, Visions of Beyond - The worse cantrips. Visions has potential with more wheels, but 20 cards is actually quite a lot
Precognition Field
Counterspell
Night's Whisper
Skull Storm
Merchant Scroll
Gush
Rite of Replication
Hero's Downfall
Dramatic Reversal - Ramp with enough rocks
Leyline of Anticipation/Vedalken Orrery
Archaeomancer
Demonic Consultation - The buyback cost is pretty steep, but I don't have to pay it until I want to cast it the second time

Considered swaps:
Thought Vessel -> Dimir Lockets

Considered cuts:
Cryptic Command - UUU may be difficult sometimes, but the tap ability can be important
Disallow - Shave on counterspells in general?
Opt/Thought Scour/Impulse - Might not need ALL the cheap cantrips
Expansion // Explosion - Explosion might just be too expensive
Tendrils of Agony - Storm could be unfun
Niv-Mizzet - Triple red might be hard
Capsize
Discovery // Dispersal

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Cuts:
Force of Will - Don't want to move it between EDH and legacy. Foil is a good substitute
Counterflux - Too many counterspells, and even when cutting this I could still win a counter war over something important
Talisman of Indulgence - Probably don't need all the mana rocks, and this is the worst one since it never can tap for blue
Visions of Beyond - 20 cards might be too much if I'm casting cards from my graveyard each turn
Notion Thief - Not a spell, doesn't affect my spells, and isn't even guaranteed to do anything
Lightning Greaves - How often do people really want to use target removal on Kess anyway? Could be used to save a Lab Man, but if they manage to kill it through counterspells, I deserve to die. Useful for Talrand or Docent, but meh
Path of Ancestry - More important in Edgar
Jace, Vryn's Prodigy - Planeswalkers are fragile
Torrential Gearhulk - Expensive non-spell
Foil - Might not have enough Island cards
Path of Ancestry - More needed in Edgar