I should give you a caveat; this is straight out of my butt with no intermediate discussion, some of it may be wrong, silly, or revised if we need it to change.
Colonies are launched as private ventures with, how should I put this... variable... degrees of preparation and planning. Some planners do a good job of providing for a minimum standard of living and others do a terrible job. A few hundred thousand people with prefab factories and some imported heavy equipment would be a middling-reasonable sort of colony. Ten thousand people living in shacks and buying imported goods from the company store (with company scrip, at a 40% markup; talk about captive markets) would be an awful sort of colony. Most fall somewhere in between.
Several colony worlds are up around the sixty- to hundred-million mark; about what you need to build and sustain an industrial economy capable of designing and building giant robots of your own. Most of that is natural increase since those colonies were settled; shipping people is expensive enough that it's easier to pursue natalist policies on the other end, although it still happens because even large colonies are hungry for labor. Some people have sufficiently valuable skillsets to get shipped from colony to colony on assignment, while others are simply there for warm-body jobs requiring the 'right' (Earth-centric) mindset.
There are a few colonial universities (like the Peloto Polytechnic College, where the Hi-Leg was developed), and many local branches of Earth, Martian, and Jovian universities on colony planets.
Past that on the scale, Shebehu, not a colony per se, has several billion Ijad and an unknown number of potential host bodies, human and otherwise.