Yes, there are supposed to be 61 cards.
Been playing this since October, will keep playing till rotation.
During "Born of the Gods" I played it more aggressive. Full Sets of Steam Vents and Sacred Foundry with Anger of the Gods and Stormbreath in the Sideboard.
Since then I've gradually pulled back on the red splash, for consistency and to take less damage off lands. I miss the red sideboard spice, but it's just a stronger deck to play to your late game with Cleansing/Quicken/Divination.
Mutavaults: I am only running one due to availability. I could really stand to pick up two more, though that's unlikely this close to rotation. I should probably add a Radiant Fountain, as the color requirements are more than met at this point.
With Rabble Red and Burn being decks now, the conservative mana-base is much safer.
Removal: Double Celestial Flare can be weak against a lot of decks but my local meta has a decent helping of hexproof, brave naya and even some heroic decks. Flare's a great hedge against decks going all in on one creature and also good post-board against larger creature decks when they try to stick one creature at a time and force you to wrath.
Sweepers: Ain't no blowout like an instant-speed Planar Cleansing Blow-out.
Countermagic: Syncopate is a necessary evil, Dissolve is the best. I miss my Izzet Charms, but they were too hard on the manabase. Counterflux was great, but the mirror isn't prevalent enough to mainboard a Cancel against 90% of decks.
Win cons: I have been very happy with 1 Aetherling/1 Elspeth. Aetherling is a virutal mulligan against anything aggressive, but it's worth it to quickly close out game in 50 minute rounds.
Have loved playing the deck this standard season, months of practice led to fewer draws despite the build gradually getting grindier and grindier. Those playing UWr always had trouble with walkers, I'm only sad that it took the addition of Temple of Malady + more Abrupt Decays to get us to switch to Planar Cleansing so late in the season!