Equips will generally go for attack based:
Nail: preferably koda (still one of the best around)
Add gear: I take h helm for now (till glory cloak is out anyway) it adds vit, atk% and some bonus atk once maxed crit. (shd be abt 35atk)
Armor: schwartz/ drag mail/ exelis
Spec: any slotted one...
Generally, what you would want is to focus on high dps, but still have enough hp for survival purposes.
By maxed level(225), you would have about 3k hp +- depending on ur type of equips..and that hp is asking to have a one hit death wish at high level mobs (roche hits physically 4k) This is what you can do...adding some stats to vit, or gemming your equips with hp or vit star ability.. (Another useful survival tip is to train 3 pets with high vit stat, and to keep summoning them out to protect half the damage you take in from ur "failed avoid".)
Yr stat will generally be CRT AGI, and dependant on what type of assassin ur aiming to be (tanky,fast skill,or pure dmg) you can add on that last stat. (If stop adding dmg increment stat, ur atk will stagnant at best around 1500 with top tier equips/ xtals)
Being this build for assassin, you must be able to face up to ninjas (who can deal higher dps than you, can take in dmg due to clones, can avoid too), glads (whose dps outclass you so badly). So that's the negative....(well until the avoid counterskill is released anyway) GoodLuckb