Sorry I've not caught your question sooner. I'm guessing you've probably found an answer to your question by now. Just in case you haven't; plant iris very shallow, I've even had some do fine just by laying the tuber on top of the soil (I did that once as an experiment). Good drainage is always beneficial to any plant so add plenty of organic material to your planting spot to help soil deal with any dry or wet conditions. I always stress having good dirt, it's one of the best things you can do to get your new iris off to a healthy start. Use iris in the back border, unless you're planting the shorter variety, and be aware that some taller varieties may need staking. As far as iris multiplying, mine don't seem too eager to replenish themselves, however, should your's need dividing, do so after flowering, when leaves and stalks have begun browning.
I wouldn't keep their roots crowded in there very long. Watch for signs of stress, and if they look sad, find a spot for them within a day or two. I'd put them where you get the most lookers, that is if you want to show them off. They're so pretty you should give them a prominent location where they'll get noticed.
Thanks' TC, part of my problem is can't decide where to plant them.
Can I just plant them iin a larger pot until I decide where to plant?
I am almost a new gardener with many vacant spots. My 1st selection is a section at the bottom of a hill & I feel will get too much water draining from my plants above the iris. What do you think?