Flat fielding will easily remove any vignetting. Even if present it wouldn't be a problem at all. Even non vignetted images should be flat fielded as no image is evenly illuminated nor is each pixel of the same sensitivity. Flat fielding corrects all of this.

Under a heavily light polluted sky a mono camera with narrow band filters will give the best results. One shot color will require very many frames to get the signal to noise ratio down. If it is really bad you might need several nights worth of data to get very deep. Otherwise star clusters, bright nebula such as many planetary nebula, double stars etc. would be your best targets. You'll need good gradient removal tools and expect color casts (especially green) to add to your processing woes. I have a friend that does very well from "downtown" Berlin. Last I knew he gave up on any filters with one shot cameras. They just meant even more exposure time. Though his mono camera can go far deeper than his OSC using narrow band filters. He's been using the OSC for color data and the mono for the luminosity layer to good results. So it can be done with enough exposure time.

Rick