At Lvl 4 take Withering Flames against a spell-based team, take Deadly Strike otherwise.

At Lvl 7 take Elusive Brawler against an Auto-Attack based team, and Gift of the Ox if spell-damage based.
Brewmaster's Balance is good if you don't have a healer on your team.

At Lvl 20 take Elemental Conduit if you wanna be able to zone, chase and damage the enemies more, Purifying Brew if they have cc effects that can mess you up, and take Energizing Brew in most cases, drinking the full duration before entering a fight gives Chen immense value, 20% health and damage is really strong and will make him tanky like few other tanks.

At Lvl 4 take Accumulating Flame for a bit more damage, or Deadly Strike for it to cost nothing, and to deal a lot more damage once you have shield.

At Lvl 4 take Accumulating Flame for a bit more damage, or Deadly Strike for it to cost nothing, and to deal a lot more damage once you have shield.

At Lvl 13 take A Touch of Honey if you can easily get Auto-Attacks in, if you can not, take Ring of Fire and just run around them letting that do the damage.