Difficulty Ratings (1 to 5)
It's hard to quantify difficulty ratings, so I'll try to give you a good description of mine:
Little to no knowledge of cars required. Little to no risk of damage to the car or yourself, unless you just got up and walked away. If you don't know what you're doing, or bail out mid-project, returning to original is simple. You may've never heard of a torque wrench.
Very limited knowledge of cars required. The project will have minimal steps, so it's easy to revert if needed. Not automotive intuition is required, you just need to remain organized and careful. You are not scared of opening the office printer. You know what the red and white RCA connectors on the back of a TV are for. You know the difference between an HDMI and USB cable.
You've done general car maintenance. You don't know what every sensor does, but generally understand how a car works. You don't mind a few bruised knuckles.
It will require some general automotive understanding so that you can troubleshoot issues as you move along the project. The project may take more than a few days, and you are comfortable with having the car down if needed to diagnose a few problems.
You're familiar with how a car works. You're not here for a how-to, just to get the inside scoop on the "gotchas" before you begin. You have a pretty decent deep toolset.