Awesome that you're already listing interesting topics! Any of those would be great. Whatever you feel most comfortable with, and what you believe newcomers to programming would benefit from hearing.
But of course, I also wouldn't want to be a nuisance to you, and your free time. The length of the talk is totally up to you, it does not at all need to be strenuous for you, 20-30 minutes is some rough outline we usually go by. My timezone is CEST which equals GMT+2, hope that's not too far away from yours. A simple Skype call or Hangouts call would more than suffice. I can organize a quiet enough classroom for everybody to hear you just fine.
Please send me a message through the Steemit chat so we can talk some more! My user name over there is also: adnanrahic