Hey Chelle,
yeah, you're definitely overthinking it for an iris--
growitall is right--that the majority of plants are quite indifferent to pH.
I will add--as long as it is not too extreme.
In my case, my soil was formed principally from alkaline parent materials (lime) a looooong time ago plus hundreds? thousands? of years of low rainfall. So we have high pH around here (mine is 8 to 8.3 or even higher--related to the amount of buried concrete I find). Our water is also very alkaline. This essentially ties up nutrients, especially iron, in the soil and we can have a tough time with even the supposedly 'alkaline-tolerant' plants. Ever seen a chlorotic siberian elm? Well, the sagebrush does alright
but I have no business trying to grow blueberries.
Rocks do contribute to the mineral and acidity-alkalinity milieu (but I find concrete to be the worst offender in exacerbating my pH problems) --you shouldn't have any trouble with field stone or whatever your flat stone is, and your area may actually be naturally acidic enough that crushed limestone could be the way to go for the western plants on your list.
Try some areas with (a little) and without compost--see what works for you.
