Hey Sebastián, I highly recommend checking out Jama Jurabaev's Learn Squared course. I'm taking the class currently it's been career changing. I focuses a lot on hard surface design with 3d Coat in a a very fast and intuitive way that works well for those working under tight deadlines. Attached is a rough sample I did for a homework assignment there. Really easy to do and didn't take much time at all.
For getting very precise edges I'd recommend switching to surface mode once your voxel model is roughly the shape that you want. Surface mode essentially eliminates the interior polys of your object so you don't have to worry about having too many polys. If you crank up the resolution of your voxel based model you will start to have problems because of how many polys you're creating, it can really overload your machine and start to slow things down. When you apply a detail in surface mode it automatically creates more polys in the areas you need it. Makes it super easy. 8x and above is probably way too high. I'm usually working at lower res so 0.8 or something. I try to keep each layer under 1M.
If you're trying to keep it in Voxel mode I'd suggest keeping it at a low resolution due to how many polys you'll be working with (each layer under 1M should be ok depending on your machine) and then using tools like cut-off and Vox-hide to get those nice even planes. That's how I created the image attached basically. I wanted to keep it low poly count since its essentially just for conceptual purposes.
Hope this helps!