Are you planning to overclock to the max to squeeze out every last ounce of performance and also to run multiple gpu? If not then i dont really recommend getting a X370 board as the difference between a x370 board and a b350 board is usually in the vrms and additional features such as more pcie x8/16 or even the ability to sli.
If you just a casual overclocker and running a single gpu on a budget, i would recommend u get a decent b850 board like a asrock b850 pro4 (not b850m pro4) and save up to around 80 usd, which u could reinvest into a better gpu or other peripherals