Seaweed,
Leader lengths are governed by time of year and personal preference: The standard rule of thumb for leader lengths is 2 1/2 times the length of the flasher. And it's a personal preference...
Here's mine for the record:
From the end of August through May, 42" of 20# leader off a 11" flasher for Blackmouth.
June - Third week in July, I add 3 to 6 inches.
3rd Week in July through August (Kings)- 4 or 5 inch spoon 48 - 60 inches with 52" as my main length.
Your next question deals with distance between the clip and flasher. Again, this is a personal preference. Additionally, there are many factors which govern this distance. Let me sum up two answers without getting you confused. For boats that are non-polarity controlled (Black Box), 20-30 feet will be about right. If you have a BB installed, 10-20 feet is in the ball park.
www.protroll.com has excellent information on polarity...
One problem with running a lot of line from the clip to the flasher is the rod losses it's hooking power. You can corrrect this by setting the line further back in the clip or doubling the line before placing it in the clip. However, your clip strength should be set at a pressure to have a small 4# salmon release.
Flasher or no flasher? For Blackmouth and Kings always use a flasher. You want to make noise in the water so these guys can find your offering. Once they hear it, they need to see it.. Use glow in the dark or colors that maintain a silhouette in the deepest of depths.
For Silvers, I won't use a flasher unless it is late morning to late afternoon when the fish are deeper. I like a Plain Jane rig early in the morning/late evening. A standard mooching rod with 2oz with 5' of leader seems right for me. The great thing about this set up is it can be motor mooched until you find the right depth. Then change weights. A Peetz slider above a chain swivel is great for this and saves time.
As far as color for Silvers. The standard green or blue 3.5 Coyotes are constant producers. Don't be afraid to try big #6 Vibrax sprinner in flo green, flo pink and orange....