I switched to Win10 over Christmas and haven't had any issues. In fact, I rather like the new GUI; seems they kept the best elements of Win7 and 8.1. Microsoft's browser, Edge, still blows though
Since i use Gmail, Outlook and Office365 web mail, local email client issues are no thing. As mentioned, a local email client is almost unnecessary nowadays and more a risk for viruses than anything it would seem
I installed full version onto a new SSD so upgrade issues weren't a problem; I've got everything backed up to externals anyways. I usually take the thing apart for cleaning and reformat system drive once a year anyways. Just cos ima nerd, yo