Yes.
Iris is a perennial plant.
Iris bulbs should typically be planted one and a half feet apart but planting them in groups of three will yield a beautiful arrangement. So yes, you can plant them in small groups.
Most gardeners plant in the spring. However bulbs and iris are best planted in fall.
I believe most iris like to be planted in full sun in most zones in the U.S. Exposing the rhizome may encourage the plant to flower.
Do not allow your iris to become overcrowded.
You need to plant iris in a sunny location.
The Iris plant is poisonous to cats, and should be avoided.
Iris has problems with the iris borer. This insect digs holes in the iris tuber and eventually kills the plant.
Iris are very hardy. However they can get iris borers and then you should dip the tubers in a mixture of bleach and water. If there are many borers, just throw the tubers away and start over. Plant the new iris in a different location.
Yes iris is a plant. It blooms in late spring but some varieties will also rebloom in fall.
Avoid plant food on the rhizome when you plant. Nitrogen can hurt the rhizome. The American iris society has an excellent web page to show you how to plant your irises. Make sure you have a sunny spot that is well drained.
Dutch iris and all irises are perennials.