Since you obviously are more into using a numpad than I am, let me run some stuff I did past you and get your opinion.
First, partly because I'm not proficient with a numpad, I also left the regular numbers across the top. So, obviously, there is some duplication there. And since it puts the zero next to the "9" key, I removed it from the lower left of that blade. Apparently a standard number pad puts the zero BELOW the "1" - or even a wider key below "1" and "2". So I guess where WT put it is as close as you can get when you only have 3 rows. But then, since I'm not used to a numpad, I figure changing it wouldn't be an issue for me as I have to get used to it from scratch anyway. In my minimal practice, I did seem to miss it a lot where WT put it and less so up by the "9".
Okay, so those number changes are one part. Next comes the things like decimal, comma (which may not matter on Excel if you have formatted the cells to include it, but would if typing text), and also the 4 basic math operators.
Once again, I do have the "luxury" of not being used to anything like this. With WT's setup, it always seemed odd to me to have one of the operators in the upper left, but the other 3 on the right column. Likewise the decimal on one layer but comma on another and it a different location.
So, for the math operators, I put all of them on the green layer, but right on the 4 home keys (+ - * /). Seemed that it would make them very easy to hit that way but, again, I'm not used to using a numpad so I could be completely wrong. The actual order of the operators certainly can be changed. I just put them in an order I felt I could most easily remember. But looking at images of numpads online, I see they typically do / * - + for the order - plus they go around a corner. I do like having them in a straight line as it seems more logical for a newbie.
I have the decimal point where you have it, but put the comma on the same key but on the green layer.
I put the comma in another place as well, where you have the zero. I forget why I did this (it is a relatively recent change), but I think I was typing something with a bunch of numbers separated by commas and found there was some awkwardness going to the green layer.
Here is a screen shot of my homemade chart:
When you see two characters on one key, the green layer character is on the right.
As you can also see, I put the math operators and some other stuff on the left blade as well. No special reason. Since I'm not used to a numpad, it presently just gives me another option. But I like some of the stuff you did there. I'll have to think about which things will work for me.
Obviously there is some room on the main layer for more stuff on the left and lots of room for green layer stuff.
So, ignoring the fact that anyone used to certain placements may not like exactly where I put things, what do you think of some of the basic concepts?