We have read several of your books and watched videos, but I was
hoping to get your insight on some great 1/2 day or full day trips
Wishing you and your bride a happy anniversary, John! You won't be hearing from Rick himself as he doesn't participate in the forums; MUCH too busy for that! Responses will be from ordinary travelers like Yours Truly and occasionally someone on staff, if they have time and good stuff to share.
As the two previous posters have said, the CT isn't really an "excursion" type of place. The 5 villages are small-to-tiny and, other than hiking some of the park's trails, exploring those villages, taking a ferry ride and/or just hanging out to enjoy the views are really the main sources of entertainment. Add swimming and sunning to the list during the warmer months, although it's not really known for its few beaches. Let's just say that most folks don't choose this destination with the intent of leaving during their stay? As also mentioned above, if you haven't booked an accommodation yet, it's past time to put the giddiyup on that as rooms book up quickly and early for high season!
Still, there are day-tripping opportunities along the coast if inclined to do so. Some travelers go upcoast to get a look at Portofino...although that wouldn't be my choice. Others head downcoast to Porto Venere, which I've not personally been to yet but read is very nice. Camogli and Santa Margherita Ligure (both upcoast) also have their fans. I'm guessing some of those fans might be along shortly with some pointers and maybe some additional ideas.
In the meantime, this is a really good website/blog for some reading up on the region, ideas for things to do, info on getting around, etc.
https://www.apathtolunch.com
Here, specifically, is a page about other towns; be sure to look them up on a map as some will be closer to the CT than others, and some might involve a car to get to.
https://www.apathtolunch.com/p/citiestowns.html
Also, if you intend to hike, this is the official website for the National Park (Parco Nazionale delle Cinque Terre) current status of the individual trails (this can change from day to day!!!), suggested routes, trekking and train passes, etc.
http://www.parconazionale5terre.it/Eindex.php
Will it be very busy in May? Yes it will: some tips for managing the mob:
https://www.apathtolunch.com/2016/03/cinque-terre-16-tips-for-avoiding-crowds.html