New Rogue Gearing Advice

[Entenei 1]

So. I don't normally play rogue - I have been asked/offered to swap to rogue for one boss where we want to cheat death a mechanic. (Xhul'horac)  Anyways I started to gear this rogue like yesterday, I know I will be going combat for the fight due to the need to kill the imps quickly.  I am unsure of what my priorities are gear wise. I did the first few bosses of mythic last night and got some weapons (daggers are not ideal for combat but better then other stuff I had (I think?))
So. For general gear/items,  I am unsure what to aim to get before mythic boss next week.  as i said i have gotten new weapons. Should i aim to get another slow weapon and put less interest on the low bits of actual gear i have.  Its unlikely i will get 2/4 set pieces Or should I drop worrying about everything else and try to get them? 
What about the class trinket I see thats very high on the bis, should I focus on going for 

that and dump my heirloom?

 

Rogue - http://eu.battle.net/wow/en/character/twisting-nether/Díxí/advanced

Tl:dr, Whats most important for a rogue with little time to gear. what should I spend my bonus rolls on.

 

(also, If I don't get a slow weapon for main hand, will my aoe dps stuffer massively and thus make it better to single target each one down as assassin or sub?) 

 

[Carrn 284]

Highest damage weapon should be in your mainhand. Not DPS, Damage. Otherwise, your offhand should be the other highest DPS option.

 

Stat priority is Haste > Multi

 

For gear, you should focus on getting a slow weapon first and foremost, followed by Mirror of the Blademaster, the Archi trinket, and set pieces.

[Entenei 1]

Thats Awesome, Thank you! 

If i fail to get a slower weapon for main hand (as in stuck with my daggers) is it not worth going combat? or would it still be the preferred spec of choice for Xhul?

 

thanks again.

[Carrn 284]

Probably worth playing Sin or Sub, since you can cleave decently well I suppose. Not sure though, I've never tried the fight not as Combat lol