How can I leave Gmail for Mail?
Before you completely ditch GMail and go just with your iCloud account, you'll need to ask yourself this question:


  Will you only access your mail solely from Apple devices?


I for one created an iCloud e-mail account on my Mac just to be disappointed that I couldn't configure my Android phone to access it. Probably Apple is not using standard IMAP for its iCloud e-mail service.

That said, you could upgrade your GMail account to a premium account to get better quality of service (and perhaps not having them selling off your e-mails).