AMD Confirms Zen3 Brings Entirely Brand New CPU Architecture, Delivers IPC Gains

No, they properly checked so they were not as affected as Intel.

Meltdown didn't affect them at all and iirc they where only affected by one of the three spectre variants.

If they can extend its use for more time more power to them. Although not sure what their mother board partners will think if its for too long.

Although, I would try and keep the same socket as long as possible. When comes to higher core counts from my understanding the current socket is showing some strain.