New PC for 5 accounts on WoW

[MiRai]

From a systems performance standpoint, will there be a difference in running two 27s uhd at 1080p versus a 40 uhd 4k?

Yes, 4K is four times as many pixels as 1080p, and requires more power to run.

I am going to use the PC listed in first post, any recommendations? Looking to spend less than 1k for the monitor(s).

All of my monitors have come direct from Korea through eBay sellers, which has plenty of risks involved, but so far it's been good to me. Unfortunately, without doing a bunch of research, I don't have any current recommendations.

What are good response times less than 5ms?

Those numbers generally mean very little, as there is no standard and manufacturers can practically put any number they want on there.

And for the hz, 60hz ok?

Again, subjective. Some people use 75/90/120/144Hz and then claim that they can never go back to using 60Hz. I've not used anything other than 60Hz, so I couldn't say.