In general you will get more help if you trim your problem down and ask specific questions, ideally attaching an example project. People helping on forums mostly do so in their free time and you don’t want to take more than necessary of that
You can’t make Eclipse WTP delegate to Gradle atm. You could use a Gradle plugin like gretty to run your webapp locally instead of using WTP. Then launching would be just one Gradle task away and other devs don’t need to setup a server in Eclipse etc.
The stackoverflow problem looks sts specific. There are tasks (launches a task only on that project) and task selectors (launches all tasks of that name in all subprojects). Look if sts has an option to do the latter. Buildship (the official Gradle Eclipse plugin) does have this option.