a) If you dont want to have issues, NO SPLITTERS, get monitor with 2 HDMI 2.0b slots.
b) there is no such thing 1ms HDR monitor. That thing is a unicorn. 1ms monitors at TN panels only.
c) There are no true HDR10 monitors with Freesync or Gsync (or without). Just gimmicks. Next year some time around Q3 there are some 28" 4K monitors costing around £1200-1500.
d) You need big monitor like 32-40 inches, pointless to squeeze to 28".
e) Imho better investment for HDR 10 quality gaming is the LG OLED 55B7V. Atm is at £1800 range, but soon it will be on sale at around £1500.
Is proper TV. Personally using the 55KS7000 with the PS4Pro and cannot beat the immersion of the sheer size. And going to sell it and replace it with the 55B7 around christmas this year for true HDR and OLED.
for answer A I have splitters and have no problems at all can get decent 60hz 4k splitters from the rainforest..
And dude as for point E) those OLED B7's sure they are 1800 and will drop to 1500 but why buy one of those when you can get the improved LG OLED C7, it can be picked up new for £1,800 too and will probably drop to the 1500 mark as well, as thats what im thinking of picking up