BHIS has a build post for an updated hashcat password cracking workhorse system. Pretty cool! It almost makes me sad to think about building a system and not use it for gaming, but it certainly makes sense if you need to crack hashes on a very regular basis. For less needy setups, the main goal is Ubuntu 16.04 + NVidia + Hashcat appearing to all work together with no fuss at all. From there, just slap together what you can afford or need or fit into your space, casewise. For me, I’ve built gaming systems for almost 15 years, all with water cooling, so I would continue to make that a necessary build piece for the quieter operation. Though, to be honest, GPU fans these days (that I’ve heard) are surprisingly quiet when new. And the all-in-one CPU cooling loops are super convenient.
Any time I’m building a system, I honestly still spend some months researching on the HardOCP forums. Been a member for so long, and it’s still a great community to ask questions of.