The trade route limit is per CIVILIZATION - not per planet. You can get up to 10 trade routes if you get the appropriate technologies and UP resolutions.
An embargo is kinda pointless since the longer a trade route is established the more it brings in. What you do get is influence with the civilization you have the trade route(s) with. That is the more his income depends on your trade with him the more likely he'll help you out, give you what you ask for and so on cause what you could do to cripple him is to kill those routes (though that hurts you until you get them reestablished with someone else).
I dont see a trade victory condition you can shoot for though if you have a lot of trade the other victory conditions should be easier to obtain.
~SDC~