I still have no idea how I'm going to build my earpieces. I'm throwing around ideas of assembling them from plastic, or carving from foam and coating with latex plaster, or bondo... yours look great, tho! Wood is an idea I hadn't thought of. I don't know what I'm going to use to make my stalk yet, either. Ugh.
Clever using the balsa wood! That stuff cuts great, I never thought to use that before.
I went to a hobby shop and found a bag of balsa pieces. All different shapes and sizes. Worked great for finding just the right thing for each component of the constructions... except the angled/curved caps. I used watercolor paper for those because the thickness had to be - well - not thick.
You can use whatever you feel comfortable with though. Any material you can cut and glue together should work. If you want to use plastic maybe you can find styrene pieces at your local hobby supply place.
As for the stalk... I had a machinist friend make mine for me out of aluminum, so I can't really help you there... other than toss out the idea I was playing with before I got it made by someone else. I was going to find a piece of 1/4" thick plastic and cut it from that. I gotta admit, I'm glad I had it made in aluminum though.