I think you have a manageable number of classes, albeit general in nature, but to go from 259 to 8 is quite an accomplishment. For "mixed-use", I think it is a problem of symbology. Once you have your symbology chosen for the 8 classes, you can combine two (or more) symbologies to show the type of mixed use (e.g. red - residential, yellow - business --- then create a simple hatch of red and yellow). Employing this for all multiple use types would only require one additional generalized class, totaling 9 classes, instead of trying to symbolize multiple scenarios for mixed use.
And if you really want to make more work for yourself, on the mixed use areas, you could calculate how much of the building (area) is used for one class or the other and show that on the map as well. the point of this would be to show the reader what the primary use of the building is (e.g. a 10-story building where the ground floor is business and the other 9 floors are residential).
It would also be interesting to overlay the municipality's zoning layer to see if it actually matches up with use