Yes
Yes
It will add a small delay that could affect your gameplay and might bother sponsors. It could also hinder your chance to rank among the top three globally. Don’t worry, it’s not a major issue. Give it a try and check out.
HDR 400 is the award given by HDR. It represents a tier manufacturers use to show they support it, even though they may not fully back it.
This screen can't show a genuine HDR picture, so it's safer to turn it off. Companies often exaggerate and take advantage of people's lack of knowledge about HDR to market cheaper monitors with HDR claims, even though the device can handle it. The panel just lacks the necessary hardware for proper HDR display, but they don't disclose this.