Vignetting is the dark top corners on the first 3 pics. This is often caused by a low quality lens at certain focal lengths and apertures, or perhaps all if it's a really bad lens. Other things that can cause this are lens hoods and filters that extend too far from the lens so they physically get in the shot. This can be fixed in post, especially if you shoot RAW.
There is no right or wrong ISO and shutter speed combo. To correct the exposure, you can correctly change one or the other, or both, or neither (change aperture instead). It depends on what you want. Motion blur? Low Noise? Depth of Field? These are decisions you need to make. Pick the two most important ones and compromise on the third, or compromise on all three. It's completely up to you.
The key is to meter it correctly. If you are shooting in auto or semi-auto, add exposure compensation once you see the histogram is showing too dark after you take your first shot. I almost always use the histogram because the LCD can be deceptively bright in dark environments like you were shooting, and deceptively dark in bright sunlight. The histogram doesn't lie, especially if you are looking at the RGB histogram (may or may not be available on your camera).
Having said all that... if you shot these in RAW, I think a lot could be done to improve them. Just some minor tweaks and they'd be good exposures.