Unsure What Motherboard & Ram for AMD 9800X3D

Hello sir or ma'am, of BuildPC community. I recent bought the 9800X3D from my local store for $428.99 brand new. I already have all the build and the new cpu will replace my intel i7-7700k. I am more of Intel cpu guy for long time and never fan of AMD cpu...until now. Few questions below I want to ask and learn:

1. I understood the difference between X870 and B850. But does the extra feature of X870 really necessary or B850 is more than enough?

2. I research and learned that never go with ASRock motherboard. The cpu will burn and damage the chip relate to bios. Does any of the other brand have similar issue? MSI? ASUS? Gigabyte?

3. I saw many people comment about the ram limit at 6000 mhz is the sweet spot relate to AMD. May I ask why? Go any higher than 6000 mhz will that cause any issue?

Thank you for checking my post and help me out. Thank you.