Your cpu should be able to achieve 60fps in all/nearly all games. GPU choice will depend largely on budget and what you want. The 1660Ti is a great choice but if you want to turn up Ray Tracing in the few games that support it then you could consider a higher RTX card.
You shoudn't buy nothing more than a 1660TI, knowing already that you will have bottleneck (10%~20%) on some CPU bound games such BF, Assassins, The Division, Hitman, etc. Still enough to get 60FPS@1080p at most games.
At least you have a 4/8 CPU. The biggest problem is for people that have 4/4 old CPUs.