Around 2 to 3 yards max.

I would say 3 yards at the most. Try playing with lofts to get proper yardage variance between clubs. I have a 15 rad gap between all my clubs. This is the most important part of loft change to irons.

Depends on how fast you swing the club, you might gain a little with the short irons then lose with the longer irons.

The distance you hit an iron only matters that you know that distance, it doesn't matter if you hit your PW 100y or 140y, it matters that you have manageable distance gaps between clubs.

Basically there is no way to tell a distance gain without some data, so to roughly guesstimate lets say you have a 12y gap between your pw and 9i, you strengthen the pw 1*, lets say there was a 4* gap.

Supposedly the loft is 80% of the distance gap, and you just took 25% of that away, so .8 X .25 = .2, .2 X 12 = 2.4y gain