What exactly do you mean by “overhead”? If it’s tied to the second question, I’d really have to say that rolling your own app can be easy or can be significantly difficult. It will depend on variables like how much coding experience you have. Groovy is fairly easy to learn if you have had really any type of coding experience. I personally have (VERY BASIC) knowledge of C++ and Obj C and can follow things I’ve seen others do. It will of course also depend on how sophisticated your program needs to be.
I’d certainly first look into CoRE as it is pretty full of rule options, and probably as close to “everything but the kitchen sink” as anything out there presently.
And of course with most open source projects with the ST community, you can adjust and tinker with the code to suit your personal needs. Hopefully finding something new and cool in your own fork that can be rolled back into the core (no pun intended) code.