You'll want 3000mhz or 3200mhz dual channel ram.
Depending on your budget:
newegg 2x4gb 3000mhz/3200mhz ram (no local warranty, risky need ship back at own expense overseas if dead on arrival)
local 2x8gb 3000mhz/3200mhz ram (if you have budget to spare)
The reason I didn't suggest local 2x4gb 3000mhz/3200mhz ram is because they're hard to find locally, and usually overpriced so much that you might as well top up $50 $60 more to double from 2x4gb to 2x8gb
Are you planning to OC your Ryzen 2600? Gigabyte b450m ds3h is not good for overclocking, but it's completely fine if you're going to run it at stock. That being said I'll suggest changing it to asrock b450m hdv for a budget mobo because the gigabyte b450m ds3h has worse vrms.
Usually the most recommended b450 overclocking mobo is MSI b450 tomahawk, good price for all the features (power phase, vrm etc). You can just change your Nexus Matx case to Nexus full atx case if you're getting b450 tomahawk.
Can consider changing EVGA BV 500w to FSP hyper k 600w since around same price and FSP has 5 years warranty compared to EVGA 3 years. Take note that these 2 are both low tier PSUs, but at least won't have to worry about your house going up in flames like those icute headway kind of joke PSUs.
Do you need the 1tb ssd though? Could consider 250gb ssd + 1tb hdd combo.
You will additionally need to buy a tower cpu air cooler with heatpipes if you want to OC as the wraith stealth that comes with ryzen 2600 is not that good. Can look at coolermaster 212, deepcool gammaxx 300/400, cryorig h7 etc. It's okay to buy second hand from other people as well, even if they've been used a long time. At most just have to buy a new fan to replace the old fan if it's been used for many years (reaching end of fan lifespan).
