IMHO, I don't think the sharpness/manual mode are the reasons for your picture quality. I think in order to improve the quality, you can look into these areas:
a. Make sure you have a steady tripod. It is a MUST for good night photography. I think your second shot is affected by the free tripod which is not steady enough under strong wind.
b. Make sure the IS is off, I can see you have done that.
c. Use release cable. If you don't have, set 2 sec delay.
d. In conjunction to (c), enable the mirror lockup.
e. Use Av mode. F number can be 8 to 16. Set ISO to 100, let the camera decide the shutter speed.
These should help. Have fun.