1- 5-10'
2- I use 6lb test monofilament, 8 foot leader.
3- Icecicles, which are just medium (3-4") minnows, or if you can, smelt.
4- I like to find fairly deep water over flats that are near weeds. It varies from lake to lake. I've caught salmon caught in water anywhere from 15 to 150 feet deep.
Also, try to use fairly small hooks, like a size 14 treble hook. And just be quiet, and get to your flags quickly, as salmon take line quickly, and sometimes spit the bait.