| If you are just returning the existing post, it should be in vertical alignment with the bridge foot, and make sure the angles are oriented to the back and top of the bass. (the bridge should be centered on the inside cuts of the f-holes) Position varies with each instrument and the tone desired, but starting about an inch or so south of the lower bridge foot edge can be a good place to start. Closer to the foot, the more focused the sound.
There are a bunch of strings (most of them) that are good for pizz and arco. I describe most that I sell on my site, and you'll find a lot of suggestions in the string section of this board. It's a good idea to review some posts for some candidates that will ring a bell when you read other's comments about them. | 
