The extended support for Windows 7 is until January 14, 2020 , from here so still 5 years to go. I wouldn't bother with Windows 8 now as it's a possibility Windows 10 might be out earlier than October. They're already changing things in IE 11 on the tech preview. I would wait until 10 becomes available so they'll possibly bring out an upgrade assistant program for 10 that will check the compatibility of your computer?
I'm running 10 on a very old laptop. Single core Celeron, 2 gig ram and a 80 gig hard drive. 32-bit version. No webcam and microphone so can't run Cortana :(