Select a slide in Normal view and type in Click to add notes below it. Show a hidden Notes pane, then read your notes while presenting in Presenter View.
Open Insert, choose Slide Number, tick Slide number and select Apply to All. Also skip the title slide, change the starting number and fix missing numbers.
To embed a video in PowerPoint, choose Insert > Video > This Device, or Online Videos for YouTube. Desktop and web steps, plus fixes when it won't play.
In PowerPoint, choose File, Export, Create PDF/XPS, then Publish. Options adds one slide, handouts or notes pages, and the web app has Download as PDF.