Thank you everyone for your feedbacks. I finally used the 50mm only. I now know that my zoom lens wouldn't make it in some situations.
For that use the 50 1.8, you'll get the best results with it for street. For architecture you're going to need something much wider, 24 1.4 or less, Especially with a 7D.
Use the 50 and ignore any shots it won't be able to take and move on. Or walk backwards if within reach.
You were right, the 50 was too long for architecture so I moved on and did only street.
I think I'm gonna save money and buy something wider. 
For night shots with my 7D and 15-85 I usually to set ISO 3200, Av mode to f/3.5, -1 Exposure Compensation, and try to brace the camera against something solid. I also generally use manual 3500 Kelvin white balance.
Very nice shots is such low light situations! 
Anyway, I'll have to try shooting more by night. Thanks again for all your comments and your help!