I'm a little confused by some of the aspects of trade routes. When a route is established, my freighter turns into a little "mini-ship" - and I know it can be attacked, etc. And it shows up on the ship roster just like all my other ships.

But what, if anything, should I do with these ships once a route is established? Should I just pretty much leave them alone for the rest of the game? Can I upgrade them with the latest model and keep the route? (And is there any point to doing this? Intuitively, it seems to me that you'd want your freighter to be as fast as possible to make more "runs" and thus more money, but I have a feeling the system doesn't actually work that way.)

Does "killing" a trade route destroy the freighter, or is it freed up to go somewhere else?

Is income based only on planet population, distance, and things that directly modify "trade" per se? I was thinking the money-making and/or production values of the planets might also be important.