Oh, gosh, no, you obviously know way more than I do on the subject! I often use soy milk instead of regular milk on a one-to-one substitution basis, and slices of soy cheese on my burgers sometimes, and shredded "mozzarella" or "cheddar" as appropriate (when I can find them) in recipes, but I've never tried making a substitute for a traditional sauce.

For me, as a non-vegan, I wouldn't think of substituting anything for the butter. I don't think dairy butter has ever caused me any problems, maybe because the amounts are usually relatively small. But I'm sure soy butter would work for me taste/texture-wise if I needed to switch, based on my experience with other soy products.

(I have a vegan friend, and I sometimes wonder if she will really stick with it for the rest of her life. Could I ask what caused you to change from that lifestyle?)