You can make the imap account default email account, but you need a pst for calendar and contacts.
You can delete the live account from the phone but you may need it if you want to sync calendar and contacts.
I would definitely disconnect the sbc account from live mail. If the mail there is all duplicated, i'd delete it.
You may not be able to do anything about the sent folders - outlook will let you select the sent folder to use and you should use the same folder as the phone. The server may not let you delete one folder though. I'm not sure why you'd have two copies of each sent mail on the phone. Some phones can be configured to CC yourself so you have a copy - but the second one would not be in the sent folder.
You can copy the folders and mail to the imap account. Is that on the yahoo servers? If so I think they can be at the same level as the Inbox (some servers only let you put folders under the inbox).
Thanks. Here's an update on my progress:
I left the live account on the phone, but just unchecked the option to sync email.
I disconnected the sbc account from Outlook.com.
I can't get rid of the extra sent folder, or the extra Trash folder, so I guess they have to stay, but I'm no longer getting duplicate sent items.
I copied the email folders and mail to the imap account in Outlook, but they didn't sync to the yahoo servers. I also tried moving a few folders into the inbox, but they still don't sync from Outlook to Yahoo. There's a folder called "Synced messages" on my phone and in Outlook under the sbcglobal IMAP account. If I put an entire email folder in it, the messages don't sync, but if I move a single orphan message (no folder) into that Synced messages folder, it syncs with my phone. That's not going to work for me. Any ideas on how to get my email folders in Outlook to sync to the Yahoo servers?
Also, how can I get rid of the live account in the Mail sidebar in Outlook without removing the live account altogether?