NPCs in this game are rather pointless. To make an immersive engaging universe, they need to have some meaningful interaction with the player that add to gameplay. Some examples:
1. Trade fleets: Offer escort mission for money. Threaten to destroy unless they drop cargo, allowing you to salvage them. Pay them for trade tips. Trade goods in space.
2. Military fleets: Offer patrol or combat support mission for credits. Get info about the state of ongoing wars. Trade weapons and ships in space.
3. Mercenary fleets: Offer combat support mission. Or pay them to employ them for a mission such as to support the player fleet or a defend a system for a month or two.
4. There can be some persistent NPCs (legendary pirates or mercenaries etc) who you can kill, or trade with, for special modified ships or equipment.
5. When you find a battle between two fleets neutral to you, offer military assistance to the highest bidder, or pick the safer choice.
Similar plausible options for smugglers, faction NPCs at bases et al.