Probably there will be a config file with some variables the user can set, such as location of the work directory, error log, and excludes file. Maybe a message in the first window telling you that you can exit if you want to edit the excludes or the config file. The installer works like that now - if the excludes file doesn't exist, it creates a default file. If you want to use a custom excludes file, you have to make sure the name of your file matches $rsync_excludes in the script.
Maybe an option to do a dry run with a report. I'll have to play with putting the output into a file and running 'du -sh' on the entries.
I can just exclude everything under /var/log/, can't I?
There are some things in the user's home that I'll probably put in the excludes file, too. Maybe commented out, maybe not. (thumbnails, browser cache, bash_history and some others.)