Well since you want to concentrate on shadow skill line and bow, here is what i would do.

Multi Target
1. Bombard
2. Volley (probably morph to scorched)
3. Twisting Path (you could do refreshing but your trying to stay away from the mobs)
4. Shadow Image
5. Up to you. You can run aspect of terror for OH **** moments. Run your siphon for health. Run cloak to save you. Up to you really. Maybe run killers blade here to give you a heal and a finisher.
Ulti. Veil of blades.

How i would run this rotation.
Send out your shades to occupy them. Idk if they will aggro onto you as soon as you send the shades. If they did, maybe choose something else?
You scorch earth them, and before it lands you need to bombard them to immobilize them and snare them. Its a amazing skill. And then get close and cast twisting path on them and then bombard lock them again. And basically just keep them bombard locked in the aoes to give you survivability while you cast a skill or 2 inbetween. Scorched earth is a aoe damage, so is twisting path. If you can keep this up, you shouldnt have too much of a problem i think.

Side note: Really effective way of healing is to mark one of the mobs with mark target and then swap to your aoe bar and do this rotation and then when the marked mob gets to 25%, killers blade him. If you want the distance, maybe use impale. Regardless, you get a 40-55% of your health healed from killing 1 mob. This uses the assassination tree but its very effective since NBs are kinda squishy. If your not getting hit coz you can maintain the immbolize lock, then you dont need this but its just another suggestion

Single target bar is probably the cloak+viel strike combo combined with DoTs like poison arrow, and maybe twisting path and maybe magnum shot to give you space. Other then that, good luck. Hope i could help