Build: Yes, since 2000. My 1st PC was a store bought "multimedia" PC in 1997 that cost me like $2000. Found out it sucked for audio. It was Cakewalk that inspired me to build my own desktop. That name brand PC was difficult/impossible to upgrade most of the proprietary hardware inside. Sort of like today's laptops ... Googled a lot about the topic, and then went to a local electronics store and came home with a box full of parts for a screaming Pentium 3. That night I had a clean first BIOS post, and the install with Windows 98 went well. Life was good! So was Cakewalk Professional 6.
Desktop: Yes, primary workstation/DAW. Also have a laptop, with my DAW software loaded for when I'm traveling. Nice to have a portable office, but I would never consider a laptop as a desktop replacement, or main rig. They are useful, though, but limiting. If my desktop acts up, I can just swap parts until all is good again. I have a twin system with the same hardware specs, but runs Linux, that I can borrow parts from for troubleshooting.
Gaming: I have never setup a rig dedicated to gaming. Not that there is anything wrong with that! I do have an older generation home theater PC in the living room, with Nvidia graphics, and a few games loaded. But I would probably get a dedicated gaming console if I ever felt the need for more gaming power. While a DAW for MIDI/audio is my first requirement (addiction), I've installed decent Nvidia cards in the past and dabbled with older games that I could get to run OK. The Intel HD integrated graphics is good enough for my use on my current rig (2014). So no new graphics boards for me lately. But I do think my current rig would do well for gaming with a fancy graphics card. No matter what, get an SSD
Intel vs AMD: I have always used Intel or Asus desktop boards with Intel CPU's. Intel is getting out of the mobo business, so I expect it will be Asus with Intel chipsets for me going forward. I have never had a mobo fail. Just my preference, but because I value stability over performance, I do not ever overclock. My theory is because Intel is bigger, they probably can write more compatible drivers. I am sure you can find forum flame wars on Intel vs AMD if you use Google.
I have always used good power supplies and keep my PC's on APC UPS power backups. Keep the fans clean & spinning. May partially explain my good luck with components longevity. I repaired a friends HP PC with a blown mobo recently. Swapped the mobo because the caps (capacitors) were bulging and leaking. The fans were also full of dog fur. Just FYI: my latest Asus mobo's have solid polymer capacitors for long life
I am very happy with my current rig. It is very fast and solid as a rock. With the SSD it reboots in seconds and programs launch almost instantly. With Sonar I mostly use virtual instruments and effects, rather than audio recording, and have a hard time pushing it to 50% CPU. DPC latency is low according to LatencyMon. My Sonar mixing latency with ASIO settings at 24/44, two buffers, 128 samples, are 2.9 msec with ASIO reported total roundtrip latency of 9.8 msec. No dropouts yet.
The only time I have ever hit 100% is with a CPU/RAM stress test called Prime95, which searches for the largest known prime number. My keyboard and mouse is still responsive, even with that running.