I'm a huge fan of fluff, and I would love to see this build get more towards what it should be to represent the Iron Warriors.
The Iron Warriors are unparalleled masters of siege warfare as well as building defensive fortifications and fortresses.[1] Right after they set up their fortifications and before the initial bombardment, they will commonly send infiltration units ahead of the main force to disable the enemy's defenses and set up ambushes and flank attacks while the main force charges the fortifications.
Vindicators were the favourite platform for the
IW, which means you should be running two. As the quote above also states, they loved to use Fortifications. Now I wouldn't go out and buy one just for this list, but if you had one on hand, I would find a way to get it into the list. There is also mention of Infiltration units, but I know we don't get those standard anymore (Chosen).
Plague Marines don't fit the theme for me either. Iron Warriors would be normal vanilla Chaos Space Marines kited out with the heaviest possible weapons (Missile Launchers, Autocannons, Plasma Cannon available???)
The Chaos Lord to me should have a Power Fist, again for fluff, not for practicality.
Just my 2ยข - Hope it helps.