Yes, you can attach the monitor to a bracket. It has a VESA mount with the 100 x 100 mm standard, which allows it to be attached to most monitor arms or wall mounts. Make sure that the mount supports this VESA standard.

Yes hdmi and Displayport.

It has no speakers

It reacts very quickly. I play first-person shooters and graphics-heavy construction games. Never a problem. I think the 1 sec. is more like 4 sec.

Well, I didn't get any accessories for it, if you take a different holder, maybe, but I don't have any experience with that.

it has an internal speaker, but since i have external speakers anyway, i can't really comment on the quality.