many of your questions have been answered by the other guys. I'll just comment on your question about the bait suspending at 4 feet...
basically you can't built such a bait. there are too many factors: water temperature, salinity, your line type and so on, will influence the rof of the bait amongst other things. a tiny change in your chosen splitrings for instance could make the bait sink to 10feet or stay on top... usually the very slow sinking baits will suspend on the thermocline and where the thermocline is varies big time.
and then there is the problem of consistency. say you mage to build one bait that does what you want. could you replicate it? as trivial as it may sound this is a very tedious task. even the machine made baits are sometime not consistent.
you could try build a heavy floater and by changing the hardware or using different riggs you could present it at the desired depth, even slow fish it over the bottom structures.
