Welcome to the forum and congratulation for publishing your book "Spring Boot in Action".
I have read the quick starter guide of Spring Boot and have some questions for you / anyone tried Spring Boot.
1) Starter Guide included examples both in Java and Groovy. Would there be any trade-off if using Groovy with Spring Boot since Groovy is "Better Java" for productivity and code conciseness.
2) How well it is integrated with IDE like Eclipse and IntelliJ IDEA.
3) I found Spring Boot Actuator quite interesting. Would your book also cover other Spring Boot modules?
Whether you use Groovy or Java (or Kotlin or Scala or whatever) is really just a preference thing. Certainly you can get some productivity and code simplification gains by using a non-Java JVM language, but aside from the benefits provided by the language itself, I'm not sure that there's any benefits or negatives from using other languages with Spring Boot. Of course, if you're using the Spring Boot CLI, then Groovy is required.
Both IntelliJ and Spring Tool Suite (which is built on Eclipse) have excellent Spring Boot support. Being an STS user, I know most about what it offers, such as a project initialization wizard (based on what is offered at start.spring.io) and really nice configuration property-name completion for application.properties and application.yml files. And there's a really nice Spring Boot Dashboard for easily firing up applications (either local or cloud-based) from the IDE. I know IntelliJ has a similar project initialization wizard (also based on start.spring.io), but I'm unsure what else it offers.
Certainly, the book covers the Actuator. As for what other modules, I'm not sure what you're asking for. But I can say that it definitely covers the top 4 main features of Spring Boot: Auto-configuration, starter dependencies, the Actuator, and the Spring Boot CLI. It also covers how to override/influence auto-configuration, how to take advantage of testing facilities offered by Spring Boot, how to set configuration properties (including profiled configuration), various deployment strategies afforded by Spring Boot, and even has a chapter touching on using Grails with Spring Boot (given that Grails 3.0 is based on Spring Boot). That said, it is very focused on Spring Boot itself, not on the greater Spring Framework and family of projects. Therefore, it doesn't go in depth on anything outside of Spring Boot any more than necessary to tell the Spring Boot story. If you are looking for in-depth coverage of other Spring projects, then Spring in Action 4th Edition is where you'll find it.