I'm coming from an iPhone as well - used Android between 2008-2014, switched to the iPhone 6 when it came out. The Pixel really impressed me, Apple got rid of the headphone jack (a dealbreaker for me), so I figured I was ready to transition back to Android. I've also been wondering whether I should set the Pixel up as new, or transfer my stuff from the iPhone. Let me know how the process goes for you. My Pixel arrives tomorrow, but I won't have any time to mess around with it until Saturday.
I got my Pixel yesterday and set it up as new. Keep in mind I am already heavily vested in the Google ecosystem using Gmail, Google Music, Maps, Keep, Google Voice, Google Photos, etc. The first thing you need to do before taking the SIM out of your iPhone is disable iMessage by removing your phone number from iMessage and turning it off. Not doing this caused me a lot of headache and a call to Apple.
Outside of that it was very simple and seamless. I'm still downloading all the same apps from the Google Play store and it takes some getting used to having been on iOS for 8 years but so far I like it. I did get a message to my iPhone from AT&T stating "Your new device requires a new SIM card to give you access to all services. Please visit your local AT&T store to get a new SIM." I am not sure what that's about because everything seems to be working fine but I may go there just in case. I believe SIM swaps are free.
Good luck.