Should I cut my plants back after the first freeze?

Yes! I grew up in Daytona and we had 6 foot scheffleras that would freeze every five years or so. They always came back.

Here are some links for you!

http://www.bhg.com/gardening/flowers/perennials/cutting-back-perennials/

https://www.thespruce.com/perennial-plants-to-cut-back-in-the-fall-1402712

In my neck of the woods it has been unseasonably warm, and the last 3 nights the low was hovering around 30°. Today it got up to 70° - so far no discernable damage to any of my plants so I am letting them be for now.

Yes, feel free to cut them back. Cutting back will help the root systems go dormant, which is what you want to happen. That will also help the plants come back in the Spring.

Although it's not ideal, it's probably not harmful.

I live in Phoenix, AZ and when we get a freeze the local nursery advised me NOT to cut back any plants until spring.

https://www.houzz.com/ideabooks/40548361/list/got-frost-damaged-plants-how-it-happens-and-when-and-how-to-prune