RE: WACO YMF
No, you would not need to retemper if you made the bends cold. I just went out to the shop and tried a piece of control rod. It bends more easily than does the music wire in the same diameter. I think that you will be okay with the music wire. You mentioned the amount of caster that you will have. I think that with the overall lightness of the model, you should be okay without any additional caster. If it worries you, build in a few degrees into the wire.
Bill, AMA 4720
WACO Brotherhood #1