Its not that confusing actually 
If you want to stay with kit lens then Nikon D5100
But if you already are planning for more variety of lenses then Canon is the way to go.
The difference in image quality of Canon 600D and Nikon D5100 should not mislead someone. Its like if Canon is 75 then Nikon is 78 in image quality.
Conclusion? .... both are really really good !!!
But ..... Nikon is a little better.
So, even if you choose Canon 600D u will be more than happy with its image quality.
A 800x534 pixel size image which is normally the standard on PakWheels cannot be told apart whether taken from Canon or Nikon with same settings. Its only 100% zoomed pixel peeping which tells you the difference when it comes to lower noise of Nikon D5100 
I dropped the idea to switch to Nikon D7000 just because of crazy expensive lenses in high quality range while i have more variety and cheaper prices in Canon.
So, for your specific case, get a Canon 600D and then u will have budget for prime and flashgun as well alongwith other accessories 
I like Khurram's idea as well. That lens will give double benefit of low light prime and macro as well. Consider that seriously.