Great, great, points. The one about "silence as a mental pause" is wonderful. All speaking courses and books emphasize minimizing "er's" and "um's" and what they often don't say is what that removing them will then leave - silence. Silence is truly a "pause that refreshes" - both you and the audience.

Another point from my own experience: if you are doing a live demo of something on-screen, be extra-prepared, and extra-practiced. Do not deviate from the practiced script. There lies madness. And maybe even have a "canned" completed project already done so if somethine does happen, you need not re-do all the steps so far. If you are extra prepared like this, 95% of the time you won't need to be. And you - and your audience - will be very thankful when the time comes and you did need to be.