I've only built Ryzen 7 systems so far, but they share the memory benefits, so get the fastest memory you can without overpaying.
At the very minimum 2400MHz, but better 2666MHz and up.
I'd suggest 16Gb sticks, so at least 32Gb total for starters.
Memory is so expensive right now, that you'll probably go over budget with anything too fancy or if you need 64Gb :(
For PSU, a good Seasonic, Corsair or EVGA unit with 700w or more with at least Gold rating.
You also missed a cpu cooler, which specific for TR4 socket. I'm always for good air, so Noctua NH-U14S TR4-SP3 would be my pick. But that depends on your local availability.
Do wait for other opinions, I'm sure many have built Threadripper systems recently ;)