For armor I would recommend shrouded as more energy really comes in handy about 90% of the time. If you think you can do without extra armors (so testing them out would be best to reach a decision)shrouded would definitely be the choice. IMHO evading damage with shadowstepping is the best defense.
Assassin attributes beside Critical Strike are ALL dispensable in my opinion, it all comes down on your build and play style. A common trade off for secondary attributes would be Shadow Arts (at least for me 90% of the time), namely because the SA line has little hard heals (all conditional) and that equally reliable/efficient shadowstepping skills could be found in the No attrb line eg. ShadowWalk, Recall, AoD. Dagger mastery is completely tradeble (ofcourse taking in account of runes) if for any reason you would like to use a different weapon than daggers eg. high critical scythe builds and critical barrage builds. Deadly Art is also tradeble although there is really not so much secondary attrb that matches or excels DA in terms of application, maybe Curses. Again its up to your build. Critical Strike is pretty much indispensable because of energy management and more dmg output although you don't necessarily have to pump it up to the breakpoint at 13 if you need points elsewhere.
Secondary profs choices are completely up to your build/play style. Common choices are A/W for IAS stances found typically in BoS builds, A/Mo for hardheals mendingtouch etc, A/N for hexes or simply just plague touch against degen Rangers, A/D for scythe usage or defensive enchantments, A/E the Shadowform farmer or just some offensive spells, A/Rt weaponspells to increase damage or survivability irremovable too so its worry free, A/R for critical barrage builds/pets
You can pretty much see that alot of variation is possible in the assassin class. SA is definitely not the only choice in healing one self, sometimes not even the most efficient even with runes. Never be afraid to explore all the possibilities in the secondary attrbs.
Lastly my favorite sin armor has gotta be the canthan 15k un dyed (black mask). I just dig those daggers sticking out on the back of my cape so much

You did never guess how much daggers I have behind the cover of my cape
