I think you are on the right track you're just using the wrong module. Xmod, Enterprise forms, Indoogrid, ListX, forms Master, Dynamic forms, will all do what you want to do and you don't have to make your requirements fit into a certain structure like you are seeing with Sigma.
One difference is that with the forms modules you would have the reps input their leads on a web form in your portal rather than sending an email. Same thing just inputing the data in a different place. The notifications and views restricted to roles are not a problem. For instance - Xmod will send email notification on form submit as well as form updates.
My suggestions for module choice- forms Master is the easiest, Xmod is next but with more power. Enterprise forms would also be a good choice. Indoogrid is good and stores it's data in regualr sql tables and has a 30 day trial - Indoogrid only if you are going to use one DNN portal due to it's expense and licensing restrictions.
Don't know your total requirements but if you want something you don't have to build and it doesn't have to be in DNN take a look at the open source Vtiger CRM project.
If expense isn't a problem you could also look at Active CRM from Active Modules. And if you have some time on your hands take a look at the dot.crm project in the Forge section of this website - due out in Oct.
Greg