Thank you for all the information you have provided.
I had previously been advised that one could not have multiple accounts in Windows 10 Mail (nor could the account be POP3) but I now see I can have up to 6 email accounts - & all POP3 provided one is careful how one sets it up - so that is feasible. This would probably solve my problems on Windows 10 laptop in a much more simple way than trying to install WLM 2012.
I now need to investigate whether one can have local folders (as in WLM) to save thousands of emails by account name & topic long term locally - which at the moment from my initial investigation doesn't look possible so would prevent me using W10M; and how to import existing emails copied from my POP3 accounts on Windows 7 laptop.
I don't use any form of Calendar in any Mail programme or App. I have no use for it.
I believe if someone has already set up Windows 10 Mail account as IMAP (I haven't set up any myself) they can't change it to POP3 but could add it again as POP3 and delete the IMAP version.
Thanks again for all your help