Designing this course sounds a lot of fun, but quite challenging. You want to make the most of the kids' capabilities and past experience, while not disadvantaging too much those who haven't had much opportunity to make (or break) things before.
I really like Clockwise_Music's list. As a teacher, I am sure you won't forget that girls are people too, and you may need to exert a strong hand at times to make sure they get a fair share of the fun and the learning. Do listen to them about the tech they want to try -- and obviously to the boys' ideas too.
Do you have to grade their work? Whether you do or not, I strongly suggest some attention to making lab notebooks. If they all have access to computers then various software solutions suggest themselves, but learning how to make and use a paper-based system is also constructive.
Do enjoy yourself. I assume that an aim of the course is to teach them the fun of doing it for yourself, so a relaxed pace is best.