Mastery - Increases maximum mana, mana regen, Arcane Charges further increases Arcane Blast, and Arcane Barrage damage, and also flat out increases All arcane damage.
Mastery is basically a better version of versatility DPS wise.
Crit - A chance for your spells to deal double damage. The more you get of this the more frustrated you get when you don't crit in your cooldowns.
Versatility - Flat damage increase and healing increase, reducing damage taken as well.
Haste - Very good, but also a breakpoint stat, once you get close enough haste to fit in another Arcane Blast in your cooldowns the sims probably would indicate that haste is your best stat until you get the required haste.
The best way to calculate stat priorities for your character is to "sim" your characterFind out how to sim
Horde: Troll or Orc
Alliance: Dark iron dwarf or Mechagnome
I'd recommend Troll unless you’re able to swap races later on in the expansion as I predict the main stat to not be so dominant when you get more secondaries, which would devalue Orc.
Due to Night Fae orc doesn't really line up, since ap is a 1:36 cooldown, which makes it synergize way better with troll assuming u can hold troll racial for 12 seconds and not losing a cast of Arcane Power.
As for Alliance, I'd go Dark Iron Dwarf or Mechagnome, and probably switch to Human later on when you get a lot more secondaries.
On a side note, yes I'm aware of the secondary stats having diminishing returns, but I think this leads to stat priorities changing. So, for example, let's say you nearly hit the diminishing returns point for Mastery, you would simply swap to going for Crit instead.
Rings - Tenet of Mastery
Cloak - Fortified Avoidance
Bracers - Eternal Intellect
Chest - Eternal Stats
Gloves - Strength of soul (generally a personal choice)
Mastery Gem: Masterful Jewel Cluster
Food - Feast
Potion - Intellect
Flask - Intellect
Oil - Shadowcore
Runes - Intellect