1) Should be fine - will probably find SuSE packages available for them. Compiling from source can be a tad difficult under SuSE until you have the development tools installed.
2) Yup, search the forums on here for extra info on configuring different media formats to work, such as .wmv and video DVD's.
3) Will all run through YaST on-line update tool, but bear in bind 9.1 is a little out of date now and patches likely to cease within the next 6-12 months (SuSE usually maintain the previous 5 releases of their distros)
4) Different management tools and graphical controls are the only main differences, otherwise very similar. They have slightly different ways of handling runlevels, updates and hardware configuration from a command line, but not much. YaST is a very comprehensive control center