The market system is a bit unintuitive, and I think there are a few things worth noting (but I think it's hard in the current version to do badly with colonies).
With the way that demand and market share works, it doesn't seem worth it to produce commodities on more than one planet (except for food). It's easy to quickly get a massive colony going (even with mediocre hazard rating) that will dominate every industry it has the resources to produce. Having other planets on top of that producing the same goods will just spread the sector-wide market value of the commodities thinner, providing an increase in income that diminishes on top of the already diminishing market share increase. In fact, the additional income from producing goods on multiple planets could rapidly flip negative for most commodities, when you consider the reduction in income on your other colonies. Food is an exception, since it has large sector-wide value and demand while the infrastructure itself for food production has very low monthly upkeep. Drugs and organs are possibly another exception that could be worth it in multiple locations, and maybe fuel.
In this respect, I think the "optimal" setup that will usually shake out is to have one open-port colony (for growth and massive organ/drug revenue) in an attractive location, with however many other planets you'd like as a single source of goods not available on that planet (if only because it's "cozy" to produce everything in-faction), plus as many low-hazard rating farm planets you can manage (whose purpose is to produce nothing but food and population income while increasing sector-wide market value for goods you produce).
Where you pick the main colony doesn't actually matter much (although hazard rating is the most important factor). Things like a cryosleeper, a slot for a comm relay, accessibility bonuses, local resources, ruins, etc are nice, but not essential. It could probably be in the middle of the sector on one of the "featureless" planets and get by producing nothing but drugs/organs and heavy industry assuming they are valid for colonies, but I haven't tried that. The "feeder" planets producing nothing but food and without defensive upkeep will be easily profitable, but will also increase sector-wide demand in drugs, organs, ships, organics, domestic/luxury goods, supplies, fuel, and machinery which should indirectly boost income in the main colonies substantially if they grow to a large population.
Another note: there's a chance when raiding a planet with a nanoforge that the nanoforge will be looted, permanently reducing their production substantially and boosting your own market share in the heavy industry commodities or fuel production. It's also an alternative route to acquire these things (plus blueprints!) without extensive exploration. It's more tempting than the temporary disruptions, anyway, since it's permanent.
And one more note: the decrease in demand from AI cores should be a strictly bad thing under most circumstances, since it'll decrease sector-wide market value for that commodity. Unless it's needed to prevent a shortage, it's probably best to never use the lowest tier cores and to be cautious about using the middle tier. However, the top tier cores provide special bonuses to certain buildings, which might be worth checking out.
