Windows 10 is a hell of an improvement from 8. You get best of both worlds, app/tile interface or traditional start menu and everything in between.
Edge is much improved and by far one of the quickest browsers out there now.
https://www.laptopmag.com/articles/best-windows-browserAs mentioned; do a clean install from a USB. If you have windows 7, your 25 digit Win7 key will activate Win10 upon installation.
If you happened to have let the upgrade run, I would still due a clean install from a USB key. Keep in mind, once 10 activates an install on a PC, its logged for life and you shouldn't need a key for any re-installations.
Most importantly, if you can, Max out your ram its probably the best you can do, hardware performance wise, on an older machine running 10.