I would like to know, based on your experience. What reports could I create, in addition to those that come in the box?
I am not sure if anybody in this SOI community have any experience in creating the custom report in jasper. From SOI support perspective we don't handle custom reporting, we only deal with out of the box reports. You'll find lot of document/guides in jasper community that should help you in creating your custom report, here is the link to jasper community "https://community.jaspersoft.com/" . You can ask question in jasper community for help as well.