You will win fps benchmarks with sli gtx1070, but your gameplay will be better with a GTX1080 at any resolution less than 4k.
You will avoid dual gpu issues such as screen tearing, stuttering, and even non support in some games.
If you wanted to plan on sli, you would want stronger than a 550w psu, more like 700w.
Your build is very good.
The one thing I would change is the cpu cooler.
I would use a noctua NH-U14s air cooler.
My canned rant on liquid cooling:
------------------------start of rant-------------------
You buy a liquid cooler to be able to extract an extra multiplier or two out of your OC.
How much do you really need?
I do not much like all in one liquid coolers when a good air cooler like a Noctua or phanteks can do the job just as well.
A liquid cooler will be expensive, noisy, less reliable, and will not cool any better
in a well ventilated case.
Liquid cooling is really air cooling, it just puts the heat exchange in a different place.
The orientation of the radiator will cause a problem.
If you orient it to take in cool air from the outside, you will cool the cpu better, but the hot air then circulates inside the case heating up the graphics card and motherboard.
If you orient it to exhaust(which I think is better) , then your cpu cooling will be less effective because it uses pre heated case air.
And... I have read too many tales of woe when a liquid cooler leaks.
google "H100 leak"
I would support an AIO cooler only in a space restricted case.
-----------------------end of rant--------------------------
Your pc will be quieter, more reliable, and will be cooled equally well with a decent air cooler.