Hey Gents and Ladies,
New to the board, looks like a great bunch of people here.
I have a question and wanted some info/opinions as to a course of action.
Here's what I have:

My boss has an older PC using Windows Live Mail on a email provider that will soon be going away.
His email was setup as POP3 and all his emails from the beginning of time is stored on this PC with a ton of local folders and such.
I bought him a new Windows 10 PC and installed Office 365 (2016) on it along with Outlook on it.
I setup his email and used Kernel EML to PST to convert and move his emails and files over to his new PC successfully.
Now here's the deal:
I want to move all his emails over to Gmail so he can have access anywhere and from any PC, among the reasons is this would give him the ability to print locally any email he chooses.
My plan is to use googles email transfer APP to move his emails and folders from outlook to his new Gmail acount.
The question is this:
Would I need to change his email from POP3 to IMAP and if so what would happen if I did so?
I did something similar to this once and it wiped out every email involved.
Being this is my Bosses PC I am being very cautious.
To summarize what I want:
To migrate from outlook all relevant emails and folders to Gmail and have Gmail pull emails from his old email service as well.
The issue is the POP3 to IMAP change.
Hopefully I painted a good picture of what I want ot do and my concerns and I hope you forgive me for my asking a few dumb questions but I like to hear from people who do this for a living as I do not do this on a regular basis.
Thanks!