Moving from Gmail doesn't mean you can't continue using all the other features of your Google account--Google Drive, Google Calendar, and so on. They will keep working with your existing credentials, even with Google Apps for Business. You just won't receive any more incoming mail in your Gmail Inbox.
Note that if you used Gmail's server-side filters to process incoming messages, you'll have to re-create them on your new provider's website, and you may have to fiddle with rules in Mail (or another client) to make them work correctly with your new account.
But most of the hassle is simply the tedium of the transfer process. Once that's done, you can relax and join me in enjoying a Gmail-free IMAP experience.
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