I know you worked hard on your setup, but I do have some concerns. Plastic worries me a bit. I know you said you bungied the pad to the underside, but plastic doesn’t leave much for air circulation over and under the pad. My other worry is the feathers. Yeah, they’re cute, but the chicks really don’t care about fru-fru. In fact, they’re very inventive about finding ways to end their little lives, and dangling feathers are a good way for them to do that. They can easily get entangled in them. Your covering should be anchored down somehow. They’ll crawl up under it, be unable to find their way out, and overheat very quickly. That can be fatal, too.
You’re on the right track, but I think your setup needs some fine tuning. Your temp should be fine….but watch them. They’ll tell you if they’re too hot or too cold. I just think you need to be more concerned with safety that cutsie. I’m sorry to be a Debbie Downer, but my first concern is always for the chicks.