I've no intention of installing Windows 10 on my primary computer, because there's no guarantee that certain programs (e.g. AutoRoute) will run on Windows 10. So the primary system is remaining firmly with Windows 7.
My back-up computer was running on Windows 8.1 until Windows 10 cuckoo'd its way onto the computer without my consent whilst I was away. It works OK, but I still prefer Windows 7 - and it took me a long time to disable most of Micro$oft's privacy-invading options which are 'on' by default.
if you've got Windows 7, I would stick with that. If you've got Windows 8 or 8.1, then I'd change to Windows 10. It installed quite readily and didn't lose any of my desktop icons or saved documents. But I had to download the Win10 driver for my Netgear 5 GHz WLAN adapter.
I archive certain Outlook e-mails to a USB stick, but ever since my Hotmail address was spammed and my Hotmail address book infiltrated, I wouldn't trust Windows Live Mail or other Seattle hippy-village 'cloudy' systems further than I could smell them!