Moving from POP3 to IMAP

I would keep the POP3 PST file as a file to open in Outlook, but not use it for IMAP.

Make a new email file with the IMAP account and use it going forward. That will work.

And what about pulls no all the emails, etc, from pop3 to imap?

I would delete P0P3 emails from the server . They are likely only kept for 14 days ( depending on Settings) . Then start fresh with IMAP.   That is what I would do

Having two sets of folders to sort through going forward?
That sounds fine for computer savvy users, but for someone who's made a big deal out of desktop icons not being in the same positions after moving to a new computer, it sounds like I'm going to need a bottle of Advil handy!

If you leave POP3 on the server as well as IMAP, there is a chance IMAP will download POP again (certainly not the first time this has happened. Pick your poison:  two folders or else the possibility of tons of duplicates.

You may want to give these articles a read.
https://www.xfinity.com/support/articles/email-client-programs-with-xfinity-email

To switch from Pop to Imap.
https://www.xfinity.com/support/articles/switch-email-pop-to-imap

Looks like Comcast has a 10 GB limit on mailbox size, so for starters I'm thinking some archiving may be in order.
Being a Comcast customer myself, I'm thinking about testing it out myself first & here's my plan.
Archive anything older than a couple of years old.
Back up pst
Create new profile & set up email account with IMAP settings.
Import pst file, telling it to not import duplicates.
I can't imagine why I would, but in the event I (or anyone else) wanted to go back to pop3, would it be that difficult? Can the imap mailbox be exported as a pst?

Your steps are correct.  

I can't imagine why I would, but in the event I (or anyone else) wanted to go back to pop3, would it be that difficult?

No. Download all your mail and turn off the IMAP account. I use POP3 on my Computer, IMAP on my iPhone and that works fine.

Can the IMAP mailbox be exported as a PST?   You would just download your mail. Yes, you can move IMAP to a PST file.

S0rry f0r the neglect, as it's been a busy week, but n0w that I have s0me 'me time', will get back t0 this, as well as finding a KB that ALL 0f the letters are w0rking 0n!

Just one more thing (in my best Columbo voice), should I delete email account n phone before starting all this?
Wondering if while this is in process, emails will be deleted from server, as they are downloaded from server t my phone.

should I delete email account n phone before starting all this?   <-- if the Phone account is POP, probably yes. But likely the Phone account is IMAP (mine is) even if Computer is POP.

Wondering if while this is in process, emails will be deleted from server, as they are downloaded from server t my phone.

I don't think so, but do the conversion first and delete the Phone account second.

Best to do this when few (if any) emails are coming in.

I archived everything prior to 1-1-16 & before deleting it, checked the file & seem to be missing emails in it.
Any reason why?
Some were flagged for follow up, but others weren't.

Have you checked all folders in the POP PST file?

It may be the user set some for deletion. You have not done anything I can see that would delete email.

Would I be better of making a pst fie & just manually moving things to it?
I'm guessing I would have to do this in smaller chunks, taking mire time...

You can certainly to that. I have done this many times.  Just keep a good backup of what you have before importing into the new PST file.

Thanks to all!