Much of this is perhaps already planned, or already in the game (when the dynamic economy isn't broken).
Just a few ideas; should apply to NPC factions as well as player.
Commodities:
Raw Materials
(produced by developing/owning planets with right conditions and deposits, and maybe smallscale mining at planets or ring systems)
Volatiles
Ores
Organics
Refined Materials:
(require the ores + machinery or something)
Metal
Rare Metal
Produced materials:
Everything else. Machinery, Supplies, food, fuel, luxury goods, etc
-To exract raw materials, refine metal, or produce other stuff requires stockpiles of crew at the market to meet labour force needs.
-To be producing any manufactured good, market needs some combination of metals and/or raw materials as ingredients, modified by planetary conditions. ie. Food needs volatiles and ore for fertilizer, + good sun and planetary conditions.
-Ingredients can come from the planet itself, or trades brought by player fleets or NPC fleets. (setting a slider for what you want to produce increases demands for its ingredients or something, and NPC fleets will respond automatically to this depending on faction relationships)
-Crew production will always happen, but higher rates require food; good planetary conditions; good sun; etc. Bonus production if you have luxury goods and domestic goods stockpiles, etc.
Ships & fleet spawning
-To create new ships for spawning NPC fleets (at faction or player owned planets) or buying in the market, there must be enough metals, rare metals, organics, and heavy machinery are needed.
-Spawning NPC fleets also require enough extra crew for sale in the market.
-When NPC fleets despawn on a market, those ships/crew enter the market/stockpiles
-The sale market and the fleets for spawning both draw on the same stockpile (military/civilian/black depending on fleet)
Trading
-Factions & Player outposts can respond to demand at nearby markets by spawning fleets to trade goods in demand there
-If relationships hostile, factions can pursue smuggling instead
-Volume of trade probably depends on size of both markets and distance from each other.
Politics and War
-NPC factions and players should both be able to colonize worlds and create outposts.
-War shouldn't just occur randomly; it should be for economic/ideological reasons
-Some goods are "subversive": Any that are smuggled, or from an enemy faction, or illegal at recieving faction, are from a friendly faction that is inherently subversive (ludd, pirates, etc)
-Or Perhaps there could be a different types of government as an attribute for each faction (eg dictatorship, democracy, republic, socialist, religious, anarchic) and certain other governments would be considered 'subversive.'
-The higher the volume of 'subversive' goods at a market, increases instability in the market, and increases likelyhood of the factions going to war.
-So even if Sindria and Indies were not at war, high volume of trade would lead to instability & possibly war, if say Sindria is dictatorship and Indies were socialists.
-This simulates the flow of people and ideas that always accompanies economic intercourse between nations, and can lead to conflict or friendship.
-Player faction ideology perhaps set by something kind of like Dominions4 scales that effect productivity
-The higher volume of non subversive trade between markets increases friendly relations between factions, especially if they share ideologoy.
-Cessation of that trade, due to say piracy, or maybe a more favorable trade route somewhere else opening up, reduces friendliness.
-During war, players & NPC factions can use large fleets to destroy orbital defenses and enemy fleets around planets
-Then with enough troop transports and marines, enemy planets can be conquered.
-Depending on faction attributes, faction may truce and/or surrender at certain points when its resources get too low, etc.
Any others ideas?