Equalising the master bus can be very effective, but in most cases it's not a good idea to correct the problems in the mix with it. It will very easily lead into another set of problems. Sometimes heavy compression and tape saturation eats the high end, so a little bit of corrective high shelf EQ might be justified. Multi-band compression can be used creatively on the master bus, but it's more common to use it in the mastering stage. Some engineers like to use stereo widening plugins on the master bus, but these need to be used very carefully due to possible phase problems.

I always mix through a limiter to "simulate the mastering" (with RMS of -9-10 db). When the mix is ready, I remove the limiter and print the mixes. It might be a good idea to use as transparent limiter as possible, so that you don't get any surprises when removing it. Just make sure the mix isn't clipping before the limiter. If the mix is clipping, you can lower the master fader a little bit. With analog consoles it was important to keep the master faders at unity gain, but it is a subject of debate as to whether this affects the bits in the digital world. I haven't noticed any difference.