You could cut almost $100 with a B450 Mobo, if you don't mind waiting for a free AMD boot kit for the bios. Or buy a preflashed B450 mobo from ebay, I found one for about $90 last month. Of course used GPU, but then you do not get a warranty. Your list looks good. idk about the HD, maybe you can pinch some pennies
Sapphire Radeon RX 5700 Non XT Boost Core 2035 Gaming Ram 960 43c Air Water Hybrid Cardboard Blower with a 20$ chinese Waterblock on the core 50 gallon tote of water, Ryzen 3700x 4.25 ghz, 15$ chinese waterblock, same tote 3200 ddr3 cl16 Team T-FORCE VULCAN TUF , B450m Asrock Pro 4 Mobo, 700 Watt OCZ PSU.