iCloud and Mail sync

I just got a new Mac and have used Time Machine to reload all the files from my old Mac. I would like to be able to work on either computer and keep my mail in sync between the two. I have mail on Gmail and an IMAP server as well as many files on my local computer organized in folders. If I turn on iCloud Mail on both computers will it keep both the same? I checked the size of the Mail folder in the Library and it is 30Gb. How will this work if I only have 5 GB of free storage on iCloud?