Here's the skinny on how to make corsages and boutonnieres from fabric flowers. I made about 50 flowers for the wedding from three different types of fabric in three different patterns: purple crepe back satin, purple polka dot chiffon, white polka dot satin. My bouquet used 18 of them, and the rest went into these.
What you need:
-fabric flowers - I made mine using the tutorial here
-glue gun with glue sticks
-spare fabric with some weight, or some felt - I used extra crepe back satin for both projects
-pin backs for the boutonnieres
I also made leaves to go behind the flowers in the boutonnieres. I think they add a nice touch that makes it more than just a flower. These are just rectangular pieces of fabric gathered and glued on one end for dimension, and cut into a tapered leaf shape on the other.