Went 48-7 over 7 runs with this deck, it's pretty good.
Aggressively mulligan for power as there's almost no aggro in this format -- though if your opponent's playing a bunch of Grenadins do the math for
Bandit Queen. The main way you lose with this deck is not being able to play your cards. I often mulled to 6 and still won the majority of those games.
Xo is the Hero choice over Vara (or Zal Chi in an FTP version) because he helps you smooth out your early game with the Treasure Chest. And if you had to mulligan you get the extra card back from him. Vara does have the potential to run away with the game, but if your opponent has any removal she just trades 1-for-1 and that's not good enough in this format. Xo is also the best card in the game right now so why wouldn't you want to have him every game?
Other cards you could substitute: the other Cargos,
Cauldron Cookbook, maybe a Banner in the market over
Smuggler's Stash?
Ijin's Choice is the pick over
Bore because you can get it with more Merchants/Smugglers, and you never need to kill two attachments anyway. It's also possible
Martyr's Chains should be in the market rather than the main deck as it's the best card in the late game.
This is a fun format - good luck and have fun!