The motherboard and other components are holding up just fine and still run very cool. It went through about a month of constant gaming while my kids were home from college over the holidays and it streams movies and TV shows nearly every night. I'm still using Xubuntu 18.04 for the OS and it has been very stable. I also set up Steam Play for playing some of Steam's Windows titles on Linux. I'm very happy with the build. I considered going with a ryzen 5 2400g and upgrading the graphics later, but I use some engineering applications and I didn't want to drop from 6 cores/12 threads down to 4 cores/8 threads. The EVGA GTX1050 has gone up in price since the holidays, so holding off might make more sense now if you don't need the additional cores/threads.
Probably, but it depends on the other components. Use partpicker to list out your build. Once you have all of the components entered, check the wattage estimate at the top of the build page. Add at least 150W to that for headroom and that should give a good estimate for PSU wattage.
Update: I received the new RAM from Amazon to replace the previous RAM that failed Memtest86. It passed initial testing.
I ended up switching the Linux distribution from Mint 19 Cinnamon to Xubuntu 18.04 (Ubuntu with XFCE) to to cure both glitchy video playback and to fix the erroneous temperature offset reported from k10temp that was preventing me from getting accurate CPU temperature readings while booted into the OS. While both distributions are on the 4.15 kernel and Mint is built from Ubuntu packages, the kernels are not compiled the same between the two distributions and I could see the impact of the differences by booting the distributions back-to-back on separate USB sticks and running both video and sensors tests. I can't stand Ubuntu's Unity interface (one reason why I long ago switched to Mint), so I went with Xubuntu, which uses the XFCE UI. I run XFCE on a number of other machines and I like the fairly simple UI, so losing the Cinnamon interface was not much of an issue. I would recommend that anyone trying very newly released hardware with Linux should consider testing a couple of different distributions using live CDs or USB sticks, particularly if they notice any performance or operability issues.
With the CPU temperature working (and consistent with UEFI/bios reported values at idle), I started running stress tests of CPU and GPU using a combination of mprime and glmark2 simultaneously. CPU temperature under stress was 70C. GPU temperature under stress was 53C. I think the cooling system works fine :)