Transitioning from POP to IMAP

I have about dozen email accounts in Outlook for Mac (Office for Mac 2011). All them use POP, but I'm planning to switch three of my most widely used accounts to IMAP. To better understand how IMAP works in Outlook, I created a 'testIMAP' account at my ISP and configured it in Outlook. I noticed a change in the hierarchy of folders.

It went from:
On My Computer
 -> Inbox
 -> other folders (that received filter POP email)

To this:
Inbox
 -> On My Computer
    -> other folders (that received filter POP email)
 -> testIMAP
    -> Drafts, Junk, Sent, and Junk (subfolders of testIMAP)

I also discovered that empty copies On My Computer and testIMAP folders were in the Deleted Items folder. I'm not sure what's going on.

What's really unusual to me, is that incoming testIMAP email goes into two folders: Inbox and testIMAP.
And POP email that doesn't have a specific filter, now goes into two folders: Inbox and On My Computer.
Cluttering the Inbox with so much duplicated email seems problematic. Is there anyway to prevent this?

Thanks,
Chuck