Γεια σας Elpiniki,
Thank you for contacting Geotab Support. To add a new dataset to the Data tab, you will need to find the data set you need from other Default reports' Data tabs. Then you will need to copy and paste the column to the custom report. After that, you need to test this by running the report in the database to se if you're getting correct results. For your request, you don't need another dataset to add to the Data tab. You will only need a formula and a cell that has 1:00:00 in hours format. The formula will use the Distance data and the Duration data in the Exceptions Detail report. You can calculate Average speed by using these two values. Please see the screenshot from an existing report to understand the formula. Please let me know if you have more assistance regarding this issue. Better yet, you can create a Support ticket with our Support department if you have a MyAdmin account.
For your second inquiry, you can run an Exceptions Detail Report for more than 6 exceptions. Risk Management report is different than an Exceptions report and it uses 6 exceptions for better usability and report performance.
Please let me know if you have more questions.
Technical Support Engineer