Yes,you should upgrade that MB.I would suggest going with a B550 instead.You get the benefit of PCIe gen4 speed,the chipset runs cooler so it doesn't need a fan and is half the price vs X570.I can't speak for ASUS but I have the MSI MPG B550 gaming carbon wifi running my R9 3900x for about 1 1/2 years and I couldn't be happier.It's built solid with great VRM and cooling.It seems to be manufactured to very tight tolerances because,unlike others I have built/repaired over the last 20 years,it went together so easy and yet fit so snug.It stays together as it's supposed to and comes apart easily should the need arise.
As for a CPU upgrade,my 3900x doesn't even break a sweat when gaming,while my RTX2070 super is maxed out.While you won't be disappointed with a 3000 series chip which will last you for years,I would suggest you get the 5000 series for the higher IPC and also future proofing.The 5800x would be my choice as far as bang for the buck.At about $400-$450,I would grab one myself if I hadn't just built this rig last year.