If I ask the question “what’s the most important thing in hitting good Iron shots from the above list”? It certainly wouldn’t be unreasonable to say they all have their importance and of course if individuals are very good at one or two things they would possibly put an emphasis on the aspects that they are not as competent on. However this been said I would hope you will forgive me generalising for the reason that I think it easier to improve by picking out just one aspect to work on and perhaps over a period of time you can build on this.
For me I would put top of the list strike quality in Irons to start with. I think this is a reasonable representation of efficiency in both our technique and skill range (co-ordination and rhythm in particular), it offers a good platform to develop from.
One important aspect from our technique in relation to strike quality you can consider is the position of your sternum at impact. If we think about a swing from a face on view point – it is common for a golfer to move the sternum position away from the target in either the backswing movement (sway) or as the swing starts its downswing with the hip area moving laterally towards the target almost in a counter balancing movement creating a reverse C position. This has the effect of compromising the downward strike into the ball.
A way to get a better quality strike that gives the feeling of more downward compression on the ball is to have the sternum position at impact over the line of the ball when looking at your swing from face on. This position is sometimes referred to as “covering the ball”. This can be very effective for those pitch shots as well.
The modern smart phone is a great way to take a video of your swing so why not get someone to take a slow motion video of your swing and check to see if you are covering your iron shots.