I have mixed expérience with this kind of company (even as private ones) where the consultancy part sucks the time and life of everyone, before - if you're luck

I have mixed expérience with this kind of company (even as private ones) where the consultancy part sucks the time and life of everyone, before - if you're lucky - some of the customer becomes dependant on your work enough that they buy you. But it's just my experience, I'm sure others managed to build companies out of side projects.