In the mid game, you want to find Kennen as your carry. He synergizes very well with Keepers like Jarvan, and after this point, level up further to find your 4 cost units.
Additional comp tips
Dusk Spatula is not required for the comp, but it helps a lot. Jhin is a very potent secondary carry, but you can also run late game units like Sett or Kayn in place of Jhin. This also allows you to drop Vayne if you go for a different carry.
In an ideal world, you would find your Chosen Dusk as Thresh, Riven, or Cassiopeia. Getting a Chosen Vayne will be fine, but won't be as useful as finding a higher cost Chosen unit.
Kennen is a strong mid game unit to run as he provides good damage and Keeper. You can also have him hold Dusk Spat until you find Jhin or another strong unit like Sett or Kayn.