The unsung hero (heroine?) of every PC: The motherboard! A good motherboard is the difference between a PC that lasts for 5-7 years, and another that you get rid of after 1-2 years. Please make sure that you pick your motherboard AFTER the CPU, and the not the other way around! This is a list of AMD motherboards, compatible with the latest Ryzen CPUs.
Please note: The best deals are dependent on rebates. Such rebates are reliable, but only if you follow the instructions exactly and submit everything on time, so better be careful!