I'll start with the last question first. This is a wild card that I can't know for sure without being there. So, my suggestion is to try a set under the component of your choice and see what happens. There is a "tell". If you put the feet under a component and the sound changes, it will eventually improve. If you here nothing........nope.
So, jumping back to the first question, you want to elevate the stock feet off the surface. Any size foot that will do that is sufficient, and yes, the 4th makes a substantial difference and I recommend it. As you mentioned, they must touch the bottom of the component. You can certainly try 3, but 4 is the earth-mover. The 4th gives you a better return on your investment for that particular component.
My recommendation is to work with the components that matter the most. The primary signal path is the best track to follow for improvement if you are just starting with these. Later, treat the power supplies with the least expensive foot that works. The general rule is that anything that plugs into an electrical outlet can benefit.
If you want to give these a try, and yes the taller the foot the better the performance, choose your dealer and tell him I gave you a money back guarantee on your 1st set. I want you to feel free to try CS2M without risk.
I've done A/B/A comparisons but it's tricky. Step 1 is to let the feet settle under a component FULLY; meaning, the sound is stable and does not fluctuate. Step 2 is to pull the feet out and go to lunch (leave the room) for about an hour / hour and a half. Step 3 is to come back and put the feet back in. Of course, you will pick and play a 5 song set to judge the A, the B and the A comparison. You won't get the full A/B, but you'll be informed by the changes enough to know that the sound would revert back to the way it originally sounded, if you leave the feet out altogether.
Believe me, it's easy to decide if you want to live with the "before" or the "after". It's an "in-your-face-difference" and you'll like it or you won't. Do not use CS2M under components with acrylic bottoms or over-damped chassis......AR Re6, ASR, Goldmund,
I hope this helps. Please let me know if I missed anything.
All the Best
Thanks for your detailed and prompt answer Joe. My dealer is a CM dealer with whom I have a good relationship, so trying the feet won't be an issue. I will report back once I have. Thanks again.