On the shocks, the stock springs are pretty soft, but ae sells a variety pack of springs in different tension rates.
As for the slipper, I have found that I had to readjust mine several times until it was fully broken in. After the third run or so, my slipper setting started to hold up well. Also, steep changes in temperature will throw your slipper setting off, as well as different types of terrain like dirt, clay, or carpet. I now realize that setting the slipper is a priority in the preparation of fine tuning the car, and it's best to do it for every run especially if you're racing.
Even more important is setting up and breaking in the ball differential. Doing so, will give your diff a long and healthy life. Here's a link that will help you with that task:
http://site.petitrc.com/setup/How2ProperlyBuildandBreak-InaBallDifferentialandSlipperClutch/
Yes, I do believe HD or Lowe's should carry de-soldering braid, or something similar.
Your build is looking great, and it's coming along very nicely! Again, good job!
