Star ⭐️ your email that you sent them so that you can easily spot when the respond. You should ideally respond to them within the same day.
2/8.They would have probably simply encouraged you to apply for the program (but didn’t mention anything about Skype call).
Gently ask them about their lab, recent research interests & what ideas are currently brewing in the lab via email so that you can mention those in ur SoP