Early on I would recommend going for the highest item level.
Once you start getting same item level pieces you can start using raidbots to sim for the best piece.
General Offensive Ranking: Crit = Vers > Haste > Mastery
Mastery is a very strong defensive stat if you can take advantage of it for certain abilities that can be dodged.
Critical Strike: Increased chance for attacks and heals to crit. Works well for Brewmaster due to Celestial Fortune which also always works on absorbs.
Haste: Increases energy regeneration, attack speed and reduces the cooldown of Keg Smash, Rushing Jade Wind and Purifying Brew
Versatility: Increases all your damage and healing done, as well as decreases all damage taken.
Mastery: (Mastery: Elusive Brawler) grants you a stacking buff that increases your chance to dodge until you have successfully dodged. Mastery also increases your Attack Power.
Just like previous expansions, the difference between races is generally very small, and therefor I recommend picking whichever race you like the most.
Some races perform slightly better for specific situations.
Dwarf for Stoneform / Dark Iron Dwarf for Fireblood if the content you run has anything meaningful to dispel on yourself.
Night Elf for Shadowmeld if your plan is to run Mythic+ and skip a lot with your group.
Blood Elf for Arcane Torrent if the content you run has something meaningful to dispel(generally Mythic+)
Pandaren: Panda can be great if current food buffs x2 outweighs other racials.
Vulpera: Bag of Tricks is a solid damage ability that scales with damage amplifiers.
Cloak: Graceful Avoidance / Regenerative Leech
Chest: Accelerated Agility / Waking Stats
Bracer: Devotion of Avoidance / Devotion of Leech
Boot: Plainsrunner’s Breeze / Watcher’s Loam
Ring: Devotion of Critical Strike / Devotion of Versatility
Weapon: Frozen Devotion / Sophic Devotion
Legs: Frosted Armor Kit / Fierce Armor Kit
Generally you would want to pick something that has crit, vers or both.
I would recommend to sim to get the best offensive result.
As mentioned under stats, mastery has its uses so this is something you will have to decide for yourself if you need the defensive value.
Phial: Phial of the Eye in the Storm / Phial of Glacial Fury
Healing Potion: Refreshing Healing Potion
Potion: Elemental Potion of Ultimate Power / Potion of Shocking Disclosure
Food: Revenge, Served Cold / Feast
Rune: Draconic Augment Rune
Weapon: Primal Weightstone / Primal Whetstone depending on weapon type or Buzzing Rune.