Hello vinraith, here’s a primer on sectors.
Sectors add to the production of a colony but you must first Annex them to the colony, and then you must also Exploit them (build an exploit in the sector for a particular resource.) Once you have an exploit built, if you’ve researched the upgrade tech, you may then Specialize the Exploitation, and also Upgrade the Exploitation.
What does an Exploitation do? It produces a certain amount of a resource, based on the type of the exploit. For example, a basic Energy Exploitation will produce 10 Energy per turn for your colony.
What do the symbols in the sectors mean? Those are bonuses. Each symbol adds 1 to the level of the Exploit for that resource. For example, if you built an Energy Exploitation in a sector with 1 Lightning Bolt, it would increase the level of your Exploitation from 1 (for a “naked” Exploitation with no bonus) to 2. If you built that same Energy Exploitation in a “double bonus” sector (two lightning bolts) you would get a level 3 Exploitation. Each level of Exploitation increases the yield of the resource. I believe level 2 Exploitations produce 20 energy instead of 10 and level 3 produces 30 (IIRC).
These Exploitations can also be Upgraded if you researched the right techs, up to 2 times total, and the max possible Exploitation is level 5. So if you build in a “double bonus” sector, your Exploitation starts at level 3 and can be upgraded to the max of 5. That’s why double bonus sectors are good.
In addition to this, you can Specialize a sector. For example, research sectors can be specialized for civilian or military research, which provides a bonus for that type of research.
In general, double bonus sectors are best but if you really need a resource, build on a single bonus sector. Try to avoid no-bonus sectors (keep in mind a sector that is “no bonus” for some resources will be single or double bonus for other resources and plan accordingly).
You can only have 2 Exploitations of the same resource per colony and there are several possible specializations. Some specializations will work well together (like the Food Farm Spec and Food Export Spec work nicely together to create a “Food Exporting Colony”) but others are entirely up to you - I often build only 1 Production sector per colony, either Military or Civilian depending on what i plan to use that colony for.
In general, if you have colonies placed where you can grab multiple double bonus sectors, that’s great but you also want to produce the stuff you need.
In the long run, energy is by far the most important resource but it’s also arguably the LEAST important early as you can get by via selling your battle rewards in the early game. However, early on you also need at least some research to get to the cool toys. Depending on race, you may also need food badly. Vanguard have a great doctrine for food for all colonies so they have less food need but some of the other factions are food-hungry. And of course, once you get your economy off the ground, you need production to build all the crap you need.
My general rule of thumb is to figure I will expand to 3 cities in the first 10-12 turns, building 1 via colonizer and grabbing one via influence. I try to scout so that I can find good spots with double bonus and I plan my first three cities depending on what good bonus sectors are available. Generally speaking, I want a food city, a research city, and an energy city in the first three, with perhaps one or two of those adding Production as they grow. Later cities I probably want energy, if I can get it. On a medium map, you can do quite well with 4-5 cities, 3 is a bit tight, and 6+ is great if you have the room but don’t over-expand.
I actually like the economy in this game.