Peat is bad for bearded iris. Japanese like acid but not beardeds. Neutral to alkaline is their preference.

I have clay and the beardeds struggle with it. Difficult to put down deep roots. I amend with organic material, adding bonemeal or bulb food (low in nitrogen). Good drainage is imperative to prevent rot. For my soil and climate, I soak the beds for several hours and not again until the top 5-6 inches of soil is dry.

During summer the iris are tired after their spring display. It's normal for them to look a bit ratty. New foliage will appear later. In zone 5 they may lose all leaves before winter???

Rooting powder is not needed. The new rhizome has all it needs to grow. It is like a storage tank. Pot culture is not very successful for beardeds - maybe a 1/2 barrel. The rhizome travels to new destinations and quickly outgrows a 12" pot. Plus their roots can grow down 18"+ (tall beardeds). After 2 years expect to redo the pot with new soil and new divisions. Maybe after 1 year for vigorous ones. Standard bearded dwarf iris or Miniature bearded dwarf iris (SBD & MDB) would be a possiblity.

Thankfully bearded iris are forgiving. If you have good drainage the winter rains shouldn't rot them. Iris borers may be the biggest enemy?