Hi. Well you can have multiple registration modules as you discussed and you can also have multiple user directory modules based on those registration modules. So far so good. Additionally you can 'Filter' the list and allow sorting for the categories but I don't believe you can specify multiple sorting fields at this time (i.e. sort by category and sub category). Within the template you can specify a mail to link which would include a subject for the email message along with other details. Another thing you might look at is our Tailored Text/HTML module. If you navigate to our Dynamic User Directory under Products, DNN Modules, Dynamic User Directory you will see an example of integrating these which might be able to help you out.