1) I'd advise sticking to DeathSentry and Wake-of-Inferno. I want max with both. (This is logical for WoI. As far as DS goes, it depends on what you want the trap to do. If you use it for it's corpse explosion, take it to the radius you like. If you also rely on it's lightning damage to take out FireImmunes/Resistant monsters, max it. DeathSentry is a hoot in the Cowlevel.2) ShadowWarrior would be more advisable than Master. Master has a tendency to cast CloackofShadows, which can annoy the hell out of partymembers. Master can also cast MindBlast, which has a % to convert monsters. If you play with a paladin, this would take over it's aura, and when the convertedstatus expires, the aura would still linger around the monster. Not nice, and sometimes downright lethal.
3) Iirc, you need to put them into the Warrior. (not sure though) Although I would advise against putting more than one point in SW. One point will give you acces to the skill. At one skillpoint, the Warrior is still a good and viable companion. Assuming you'll get +skills equipment, she'll get a boost from those. This allows you to put more points in other skills.
Put 1-5 points in BoS, seeing how Attackspeed influences your castingspeed of traps. Have a weapon with fast or veryfast attackspeed. (this is no problem, seeing how every claw has that AS)
Personally, I like to put some points in Venom, to take good care of Fire+Lightning immunes. (If you're lucky enough to find a ITD claw, I was ) The 'of piercing' suffix can appear on Katars from Clvl 25. (as well as daggers and rods, though a rod hardly seems "Lurkyshadowfigure" like. )
If you're going for dualclaws, only stick a few points (1-3) in WeaponBlock. This will provide you with a nice blocking, though not enough to cause blocklock should you get covered with monsters. (which is a situation you should overall prevent ) Again, +skill items will boost this skill further, and prevent precious pointspending.
Damn, I love this class, I got a bit carried away, probably more than you wanted to know. I guess I'll be writing a Traps Assasin Guide afterall
It doesn't matter wether you run or fight, you're either judged as the coward or the fool.