1. 8700K does not come with a cooler. You need one.
If your case(which you also need) has 160mm available, the noctua NH-D15s is as good as it gets.
2. Do you need a sli capable motherboard? sli is not recommended when a single card will do the job.
A number of Z370 motherboards are priced around $140 cdn.
All Z370 motherboards will oc decently.
Most 8700K processors can get near 5.0
I would not worry much about overclocks, the 8700K is a beast at stock.
3. A GTX1080 generally needs only a single 8 pin connector which can be supplied by a typical 500w psu.
Your amp! card is a heavily overclocked version that needs two such 8 pin connectors.
650w would do it, but I have no problem with a bit of overprovisioning.
The EVGA G2 is a top card.
I might suggest the Seasonic focus 750w unit for less, on sale now for $95 after rebate.
Modular, compact, gold rated with a 7 year warranty,
https://www.newegg.ca/Product/Product.aspx?Item=N82E16817151201
On the graphics card, I generally do not like the maximally overclocked versions.
I think it is better to buy a basic GTX1080ti instead.
But, I think you are ok
As to zotac service, I can't say. I like EVGA better.
What will be your case?