At the moment all we can say is that if you take the same tier board (eg Crosshair Hero), the x570 version will be more expensive than the x470 version (how much more expensive remains to be seen). For the extra money, you get a more beefy VRM and PCIe 4.0 across the board (so all PCIe and m.2 slots). With x470, you get a weaker VRM and PCIe 3.0 on your CPU-driven slots only (so the 16/8x slots and 1x m.2 slot), with all your other slots and m.2s being PCIe 2.0.
For your use case, the main advantages of x570 would be the stronger VRM if you're considering upgrading to a 12 or 16 core at some point in the future and the ability to run multiple PCIe 3.0 or 4.0 m.2 drives at full speed. I'm planning on a 3700x build and potentially switching to a 3900x or 3950x when the next gen hits.