Getting an i5 8500 would requite a motherboard upgrade too.
I would also say it's better to get a GTX 1060 with the i3.
Get the GTX 1070 if you plan to upgrade to a good i5 at some time and be aware that you won't be able to utilize the GTX 1070 full potential with the current CPU, especially in more CPU-bound games like most open world games.
Getting an i5 8500 would requite a motherboard upgrade too.
I would also say it's better to get a GTX 1060 with the i3.
Get the GTX 1070 if you plan to upgrade to a good i5 at some time and be aware that you won't be able to utilize the GTX 1070 full potential with the current CPU, especially in more CPU-bound games like most open world games.