Hey there! My name is Lynxis and I also use Windows 8.1 Professional. It's a great operating system! It has some network issues here and there, but all can be fixed with the trusty command prompt. I like it better than Windows 7, as long as I have a program like IOBit's StartMenu8 to give my start menu a bit more customization.
Anyway, for a mail client, Thunderbird is pretty nice! On my mobile device, I usually use Outlook, but it's up to you. Also, for painting, I don't think Krita is worth downloading if you already have Corel Painter. My friend has Corel Painter 2017 and it looks SUPER nice. I look forward to purchasing that software in the future.