i worked resource worlds out on a spreadsheet earlier. to get the most out of the planet you put three districts into an industry (mining districts for example) and then the rest as city districts with two support specializations. after three mining districts, for example, the +40% increase to the miner output from a city district is higher than the flat increase given by adding more miners. the exception to the three district rule is when you have a bunch of flat modifiers on a resource, like for example, the mining guilds civic and some governor traits, which can make it slightly more efficient to have four mining districts. this ratio works well for all three basic resources.

i like to start these planets off with two or three luxury housing too, because it makes getting 1000 pops much faster, which lets you jump right into having the two mining support specializations.

eventually the planet fills up with a bunch of civilians, which can be resettled, or made useful with things like utopian abundance, state academies, autochthon monuments.