Kinda seems like you're doing too much here. Karador is not just a reanimator commander but he's a combo commander and very easy to get momentum going should no other player in the pod have graveyard hate. Just as a precaution, I would throw in an Elixir of Immortality just to protect your graveyard. I'm also not seeing any dredge cards in your deck which are big in Karador. For planeswalkers, the only two that come to mind that do really well in Karador are the Vraska you have already and Liliana, Death's Majesty. You want creatures that do things when they die or enter the battlefield. Like Ashen Rider or Kokusho. Also Mikeaus, the Unhallowed with Triskelion wins you the game.
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Narset is a must in this deck. She prevents your opponent from drawing additional cards and does the same ability Search for Azcanta does. Your creatures are a bit off for UW control. Most UW decks want maybe one or two creatures that are difficult to get rid of. I honestly forgot all about Cyclonic Rift for my own UW build and I need to add it in but it's at least a one of and that's it.
You want more than two mana gems that's for sure. Sol Ring is one of the best ones and is an EDH staple. Thran Dynamo is another and Gilded Lotus too. Worn Powerstone is another. I run at least 7-9 mana gems. Spine of Ish Sah is a decent artifact that deals with a certain permanent and since you're playing blue I'm sure you can find ways to bounce it.
Majority of commander decks run at least 2 to 3 cards that give them an unlimited handsize so if they have those out then they wouldn't have to discard but Jin-Gitaxias is still amazing and is by far my favorite Praetor. You might want to add some artifacts that can destroy or exile permanents because if someone gets out Iona and calls blue your deck is dead.
Surprised to see a UW control list for modern. I was always told UW runs too slow for modern. How does it work out?
I put mine up if you wanted to compare. http://www.mtgvault.com/alphazulu88/decks/nivmizzets-ideas-edh/
Idk I run 36+ in all my decks.
I only run 11 creatures in my Niv deck and I have a bunch of infinite combos in it as well. I'll post a link once I get mine up also. I feel like with 5 artifacts the deck is too slow. You don't have Sol Ring, Thran Dynamo, or any of the other decent mana gems. Also why not throw in Omniscience? It's one of the best cards around for this deck.