"On my mac" vs iCloud... How can I get my system in sync?


play thing
I've just replaced my MBP's HDD with an SSD and upgraded to Mountain Lion in the process. I'm (desperately) trying to keep the new drive as clean as possible while adding just the old apps and data I need – rather than adding everything from the old drive drive (now re-homed in an external enclosure).

The OS on the old drive had been updated a few times and seemed messy. The chief reason for this is Apple's migration from iDisk to Me.com to iCloud. It left me with stubborn iCal items that refused to be deleted, duplicate address book contacts, etc. And, in truth, I've never really understood the whole "on my mac" vs on the web thing. I never felt that I had any control over where things end up.

Can anybody offer advice on simplifying this?

I want to merge my existing "on my mac" content with iCloud, and ideally switch off "on my mac" completely. I'd like a single data source for Contacts, Calendars, Reminders, Mail and Notes, that resides on iCloud and updates all of my devices. Isn't that what it's supposed to do?
/Applications/Utilities/Migration Assistant? Plus in 10.8.x with iCloud just use (to get iCloud stuff/Sync) with the free iCloud use System Preferences->iCloud pane.

Plus in 10.8 IMHO don't use Mail to important email servers. Just use System Preferences->iCloud Pane to see it up and pay attention to the iCloud web site with this new 10.9 iWork stuff coming down the line.
I tried using System Preferences->iCloud pane. I checked the Mail checkbox but every time I restart the Mail checkbox is unchecked. Next to iCloud in system pref's there a blue @ icon for "Mails, Contacts & Calendars". iCloud appears twice in that at window: once with the silver cloud icon and once with a blue @ icon which I think is the old MobileMe graphic. I'm confused.... I thought iCloud had resolved all of these issues.