As I always tell everyone, almost any info you seek can be found simply by visiting the VDCW, where you can easily find info about textureshadows (there is also a tutorial linked on that page)
To quickly sum it up, textureshadows has absolutely nothing to do with using the blocklight brushes.
Blocklight simply works by placing the brushes, setting a low lightmap scale, and casting light to project shadows from them. It’s that simple
Texture shadows only work with models. Meaning you need to convert any brushwork you want to cast textureshadows from, into models, and add a line in your custom rad file to tell the engine to use that models alpha channel.
You compile in expert mode, or simply add the -textureshadows parameter to vrad, as well as a custom rad file and there you go. Obviously you still need to use the correct lightmap scale and fine tune your lighting so that the shadows are not cancelled out by nearby lights.
If you want to continue talking about textureshadows past this point, I suggest making a new thread, where myself and others can easily help you out. Or PM me. Though I highly suggest just making a new thread, to not clog up this one, and so others can learn as well.