I want to play games like league, csgo, dota. And for homework is it better to use ryzen or kaby lake i7, and for gpu which one should i get geforece1080ti or 1070 is good?
you do not need a 1070 for those moba games, 1060 or 580 would do. ryzen would help in your homework, and would only have a small impact on fps, so i'd go with the 1700 or 1800x.
For what refresh rate and resolution? You don't need either of those CPUs. A Ryzen 5 1400 will be more than enough even for 144hz in those games. As for the GPU you probably won't need anything over an RX 570, but does depend on those mentioned factors.
Either would be fine. Those games are not demanding. an i5 with a GTX 1060 would be great.
Want "extra" power, then I'd go i7 + GTX 1070 ( the exact configuration I have). Good balance of power and price.
What kind of homework are you doing? Cad or graphic design? If you really aren't doing CPU intensive homework then either will do. Neither is going to be better than the other.
I currently am running with an i5 + GTX 1070. I can run all games at Ultra settings.