Using an OLED for a PC monitor isn't going to work out well for normal tasks, but for gaming it should be great. There's no way to turn down or minimize the ABL, it is what it is. There's a way in the service menu to turn off the feature that will dim a static image after a minute and a half though, but the ABL will stick kick in regardless. Since the monitor is pretty big, you could always web browse in a smaller than full screen window and perhaps have a dark desktop image. Should help but not sure to what extent.
I would say if it was always dim it'd be pretty easy to eventually get used to, but as soon as you do something and the brightness increases again then dims it would be rather annoying. And no, apparently having your brightness turned way down will not reduce ABL, it will just dim even further.