Users Versus Subscribers

Right now: I have e-mail subscriptions through JetPack. It works great.

Next: I want to create form so that people can contact me to ask for business through a form. I want people to be able to put in both their e-mail and their phone number and send me a message about what they want to talk about. I would like to give people the option to click a box to additionally signup for the blog.

What I’ve Done: I created a Jetpack form that is 95% to the goal.

Future: In the future, I want to provide extra content to e-mail subscribers. I was thinking of having hidden content that only subscribers (or users?) can access.

Questions:
1. Should I convert all my Jetpack subscribers to WordPress Users with the Subscriber Role?
2. If I do this, is there a plugin that sends them e-mail the way that Jetpack currently does?
3. Or, is there a way to maintain both lists and somehow integrate them?
4. Any other helpful advice on creating users versus keeping a subscriber list?

The page I need help with: [log in to see the link]