In my opinion 16GB RAM is too little. I tried this and even with 4 accounts I was pushing the limits and it was already starting to throttle (Even without running anything else, Windows still uses a pretty decent chunk of memory on its own).

Also keep in mind that WoW is not GPU heavy so you can get away with using budget/older GPU's. You will just end up playing with low quality. Personally this should not really be a problem as most budget cards of the latest 2 iterations are pretty decent (and with AMD catching up and sometimes even surpassing Nvidia you can get them pretty cheap). You may not play maxed out at 4k but anything normal use should be fine.

Other then that, go with what Jak3676 said.