Still wrapping my head around this game...

I built my first freighter this morning; after travelling to the nearest planet, I discovered that I was unable to move the freighter on top of it.  I eventually figured out it was because I hadn't built any trade buildings on any of my planets.  Once I built one, I was able to trade.

I still have a few questions... when I made the building, I got a message about a monopoly.  Does this mean that only that one planet can trade the goods in question, or that only one player can trade them, or is it meaningless flavor text?

Also, once I was able to move my freighter to the planet in question, I got a diplomacy dialogue with the civilization who owned the planet.  Is whatever deal you get here the only thing you'll ever get for the route, or are there periodic boosts in your economy?  I had figured that I would get a certain amount of money per turn based on the distance of the route (it implies this in the video tutorial), but I had to go to work at this point, so I was unable to see if this is the case.