breadpug :
https://pcpartpicker.com/list/th68sZ
Rx 580 is pretty even with the GTX 1060, beating it out in some titles. 8400 and 2600 are very similar as well, 8400 is slightly better for gaming, but I don't see the price gap being worth it. Added and SSD and bigger HDD. More RAM and better, fully modular, PSU. Added three case fans because Eclipse comes with one pre installed and three empty slots.
allow me to break down your build there.
CPU cooler is not necessary since the Ryzen CPU comes with the Wraith cooler and is good enough for some light overclocking.
Unless it is confirmed that the B350 motherboard you picked ships with an updated BIOS to support 2nd Gen Ryzen, the user you are suggesting it to will not be able to use their system once it's put together. The only hope they would have is to find someone local with a 1st Gen Ryzen chip that could help them out to update the BIOS or reach out to AMD for them to send a first gen chip in the mail that he can use then he sends it back.
That PSU is sold out and there is no confirmation of whether or not it will come back into stock. And if/when it does come back into stock, it won't be on sale anymore and will cost about the same as the one I provided in my build.
The SSD you chose is not only more expensive than the MX500, but also not as fast and reliable. Performance is lesser than the MX500.
But switching up to the RX 580 isn't a bad choice.