Becoming highly skilled at a specialty niche or dabbling in a variety of skills are both valid career paths. You just have to find what best suits you.
Keeping your company simple and stating a specialty could end up making your business last for generations.
Doing some research, keeping an eye on competition and talking to other plumbers can help you home in on your specialty.
Specializing in one service could be the way to see your company grow its customer base easily.