Upgrading is a great idea. Professional email is more robust than just IMAP, it's Exchange/Office 365, the backbone of enterprise email across the world.
I wouldn't say seamlessly. The best thing to do is create a .pst backup of your current Outlook email. You'll simply import that .pst when you change over. Or, GoDaddy can migrate it for you for a nominal fee.
It can be setup as IMAP, but that would be a downgrade from what it comes as. Exchange/Office 365 if far more robust than just IMAP, but the choice is yours when setting up in clients. Setup in ios devices with Exchange is super easy. All you need is your email address and password and then you're done!