Switching from iPhone 5 to Nexus 5 (US AT&T)

I bought a Nexus 5 last week because I'm really interested in having a bigger screen and I've never had an Android phone. Ideally, I'd like to freely move back and forth from my iPhone 5 to the Nexus 5. I've ordered a nano-to-micro sim adapter, which arrives tomorrow. What kind of bumps in the road can I expect? The guy at the ATT store thought it would be relatively straight forward.

Other facts: I'm grandfathered in to unlimited data on ATT, and obviously hoping to utilize LTE on both devices.