I think you implied this in your question, but just to re-iterate there are three things you need to consider when figuring out the current handling capacity of a trace/track.
1) Obviously, the width of the track, measured in mils or mm.
2) The thickness of the copper, measured in ounces per square foot
3) The length of your trace/track.
Also bear in mind that you the maximum current handling capacity of your trace/track is where its dimensions are the smallest. Kind of like the saying, a chain is only as strong as its weakest link.
You can search google for "trace calculator" and a whole bunch of them will pop up.
When it comes to copper pours, as FvM said, "Make the trace width greater or equal the calculated minimum along the current path." So first lay down the trace and then fill the area around it.
Remember that whenever you pour copper and let's say there is VCC on the top layer and GND on the bottom layer, you are de facto creating a capacitor. Moreover, if you have a long trace ending in a copper pour, you are creating an antenna. I sure you can see the problems that both will bring.
Hope this helps. Good luck.