How much do you get paid? It's obviously your choice on how much/when you want to spend your money. But if you can wait, obviously saving up more for the best possible base system is a smart idea, because it will give you more performance, and will save you more money in the future when upgrading.
For example, if you got the i3 now, you'd have to upgrade that as well next time you want a better GPU. But if you got a decent i5, you wouldn't have to worry about that.
Also, a 500w PSU is great now, but there's a possibility you may need a 600w one in the future for new hardware, and you'd have to change that too. Etc
If you want to build it over time, you could actually build a usable PC with the CPU, PSU, Motherboard, RAM, Case and an SSD. Then you could add a HDD and a GPU after to start playing games on it.
But as it is, that build with the i3 and GTX 1060 would give you some awesome, very high 1080p performance in all games. So don't feel like you need to spend loads more to have a great gaming PC.