Microsoft ends Win 7 support on January 14, 2020. You WILL have to upgrade sooner or later. You do not want a PC with internet access to have Win 7 after that date.
Windows 10 is fine, many pros and the only major cons is the 100% disk usage bug and the poor method of auto updates. 1809 is now stable so if you install that version you will be ok.
With your PC I would not drop any major coin but grab a 580 8gb as mentioned earlier for $200. Plan on getting a new PC within a year and budget for $1000+ on that build.
If it were me I would not do anything major to your current rig. Modest card with lots of VRAM should suit you fine. My son runs a 470 and it handles everything he plays just fine so a 580 should be perfect.
I personally only run Nvidia in my PCs but if I was anticipating doing another build in the near future and wanted some extra horsepower in the GPU department till then than the 580 would be my choice at the $200 price point I have been seeing.
https://www.newegg.com/Product/Produ...8gb&Submit=ENE
“We are the music makers, and we are the dreamers of dreams.”
“We are the music makers, and we are the dreamers of dreams.”
Nvidia GeForce GTX 1070 Ti. Check this, definitely a good card for a gaming PC.