This is similar to the common bottom fishing set-up for trout in the Columbia and Kootenay Rivers in the Castlegar area. The weight line is typically lightif its snaggeder than the leader line so you can snap the weight off. I always used 8# test for everything - mainline, leader and weight line. To weaken the weight line near the weight I would mash the line a bit with my teeth to ensure the weight would break off. The leader line is usually 4-6 feet long depending on the current and the weight line less than a foot long. Now this was used when mini marshmallows were used and the bait floats.
When we used just cured roe, the weight line was 4 feet long and the leader about 18-24". That way once the weight hangs up on the bottom, the roe would swing downstream, away from the swivel and mainline. This way the roe stayed off the bottom so the trout and bulls would could find them easier and keep the mudsuckers off.