They said in the video presentation yesterday that the rectangle tool was not just for pipes and it was good for hard surface modeling. There's also the new linear align and radial align tools for UVs.
By default, the height channel blending mode is Linear Dodge(Add). You can change it to normal if you want your new detail to override the layers underneath.
Also, uv unwrap is generally done on your finished production topology but, pipelines/workflows are not as linear these days as they once were and iterations up and down the pipe are the norm.
Great work but I think the gradient from dark to light wood in some of these is too linear and blurry. Maybe try to get a bit of variation and noise into that mask.