Spawn trade fleets for trade routes.

I like it. Especially the piracy aspect it opens up. And also it just makes interesting things happen on the map. But I have some suggestions to your idea.

1. Instead of having freighters fly on their own (5 seperate ships if you have 5 freighters) make them in to a single fleet. This makes it less messy and opens up the possibility of my other suggestion. 

2. Escort fleet: Similar to linked units in Civ 6, make it possible to assign a fleet to escort the freighter fleet for a trading company. This would make the fleet unavailable for other tasks (perhaps with a cooldown to switch assignment to make it available for general use again). In the case of upgrading the fleet, make it tick every time the fleets return to the trading company headquarters.

My suggestions to your idea is about managing the weakness that an actual trader fleet/fleets. I personally also think they are just cool suggestions, but I would be biased like that.

Also, have you thought about how freighters would be upgraded? Capacity for higher income but also higher risk? Defense (especially in the case of not having an escort fleet).

If you like my suggestions feel free to include them in your idea if you want to. Whatever you want to do though.

I like the first part about having all the ships be in one fleet for cleanliness, I think any escorts would be with the fleet not following it. Preferably I would like to hide q-ships in the fleet when attacked.

As for upgrades I assume it would just be another ship in the designer, with custom support modals from each era. And again a q-ship variant of the cargo ship.

Now that I think about it we do have that design for the colony ship that rarely gets used or anything else. It could be used as the freighter itself.

I like the idea but one modification.

If you destroy the freighter then you get around 75% of the income it would generate.

This is still a significant number but I am sure some cargo will get damaged / destroyed during battle.

A nice idea. I was wondering if you really need actual fleets, or only an option to make enemy trading routes visible and the action to intercept those fleets on their route with your ships whilst waiting a few turns somewhere on the route? This might help to keep the empire a bit less crowded.