Running drives over usb is completely wrong. It will never match sata latency and performance and causes cpu load for packet juggling. On the topic of the power supply just google “psu efficiency curve”, they operate best at ~50-75% load and a beefy psu won’t run its fan.
The one thing I’d look into is x670 vs b650, you save a little money (b650) but the extra 8x pcie lanes may be useful for you in the future. At least it was for me going into Ryzen with an x470 and now on x570 with dual gpu’s and a 10g nic.
You said in another comment the price is fine so other than being fun overkill it’s solid. I have a very similar build but last gen (5950x, x570 taichi) but with 128gb ram, 3070/1070 and a power hungry 10g nic. Its 1k psu is overkill even for this with plenty of hdds/ssds attached as well. The power supply was better fit for the original 350w idle dual Xeon monster I had ages ago.
Cheap, used, yours or a friend’s old computer case stuffed with some cheap Amazon or EBay hdd drive cage (~$40-90). I’ve had a 15y/o case a coworker gave me with a cheap 5 slot cage placed where the 5.25 bays used to be for at least 5 years now. The real place to spend money is on a quality psu to run the thing.