Welcome to Zoo Admin.
1) The paths in ZT are already angled. So I assume you mean at other angles. Although it would be possible to do the graphics, they could not be used in that way. Guests, staff, and animals can only walk at the angles that they do already, as well as horizontally and vertically.
2) A true type of new zoo staff cannot be made because the routines that the staff perform are built into the ZT program itself, rather than external files. It would be possible to have the staff use different graphics, as was done in the Tour Guide Visual Makeover (
http://www.zooadmin.net/ZT1/index.php?topic=1113.0). So it would theoretically be possible to have a tour guide look like a mascot. However, they would still do the tasks of a tour guide and guests would follow them as a tour guide. Also, changing the graphics for ingame staff and guests is not easy because the selection of skin and hair colors is done within the ZT program itself.
3) As mentioned, there are many user made buildings that have music played when guests use the building. It is also possible for scenery, such as fountains, statues, and rocks, to have music or other sounds that play continually. A couple examples are the Golden TexGnome Statue (
http://www.zooadmin.net/ZT1/index.php?topic=774.0) and Musical Habitat Statues (
http://www.zooadmin.net/ZT1/index.php?topic=350.0). Musical rocks were also done, but the download site is still being worked on, and that download is not back yet. Music for buildings will work in all ZT1 versions. Unfortunately, due to a mistake in the original ZT, sounds for scenery will only work in the expansion packs and not in the original ZT1 program.