Am I crazy for doing this on a 65 Barracuda ?

Well, you did ask. I do not like satin paint on cars. I think it is what people do when they don’t want to do good body work and they don’t really care what it looks like. I think it would be a big mistake to paint your car with satin paint.
Mine will be flat black. They look good.
You can use Flat Clear over any color you want.