Mod The Sims - Normals and speculars

I'd like to ask these questions at Sims4Studio, but the registration process there has not worked for me and I see no way to contact the mods for help in registration. So anyway, I'm asking the questions here.

I understand that the normals and speculars can be imported either as .dds or as .png: I have only paint.net, which doesn't do .dds, so I'm saving in .png.

1. Most people when they talk about normals are talking about CAS parts, and they go through a rigamarole of exporting their diffuse texture to a program that renders it in a bunch of odd colors which they then convert back to black and white. But the image that produces is very different from the kind of image I'm seeing for the walls (very dark for one, and opaque for another). I can produce a wall normal that looks like the ones from the game by adjusting for black and white, brightness/contrast, & a little blur to reduce the effect of wood graining on the normal (I don't want the wood to look like it's all dried out and falling apart). Is this okay? It looks okay.

2. Transparency! The normals I'm looking at from the game are transparent. I looked at layer properties, though, and paint.net thinks they are at maximum opacity. Of course I want to save the wall normals in the correct transparency, so do I just eyeball it and set the transparency so it looks the same? I tried changing the blend mode but that does nothing. I thought I used to have in the old Paintshop before it was nerfed a way to save an image as a transparent something,. What should I be doing here?

3. As to the specular: this governs shine, correct? I see that some maxis walls have a completely black specular, which I guess would make them a completely matte wall. Since part of the walls I'm working on now is polished wood, wood that mean I should have those areas of the specular image be lighter in color--say a charcoal grey rather than an utter black?

Thank you for reading my anxious questions.