Migration to GA4

Hey all, a few basic questions regarding GA4 that I hope someone could help with. :)

1. When we set up GA4 on a blog, should we UA code, or is it needed?
2. What are the other best practices one should remember while migrating?

P.S. I don't have massive traffic getting a website but a blog with 100k traffic. But I'm looking forward to exploring GA4.