Here is what I have done in the past....
- Longer than a second - about 5 seconds in order to get multiple bursts.
- Low ISO for low noise - about 100, but don't be afraid to bump it up if you need to capture more light
- Somewhat based on the lens but an aperture to get good depth of field - about f8
- Lens depends on your location. If you are right there, then wide angle. If you are a distance away - then a longer focal length.
There is going to be some balancing going on, in terms of the shutter time and the aperture. You want to get a good depth of field, but you also need the light, so if you need to bump up the ISO then bump it up in stages. The location also contributes. If the location bounces a lot of light around as opposed to a very dark open area. I have also seen telephoto shots from a hill, with several fireworks demonstrations going on in different locations. It has a wonderful 3D effect.
Also, consider setting up for burst exposures, so that you can just lock the remote shutter release and take continuous images - especially at the end with the grand finally.