Go to Settings -> Privacy, and slide many (most?) things to off. Including Diagnostic & Usage Data to Basic.
Settings > Personalization > Start and slide "Occasionally show suggestions in start" to off.
Settings -> Personalization -> Lock Screen and slide "Get fun facts, tips, and more from Windows and Cortana on your lock screen" to off.
Settings -> System -> Notifications & actions -> "Get tip, tricks, and suggestions as you use Windows" and "Show me the Windows welcome experience after updates and occasionally when I sign in to highlight what's new and suggested" to off.
Go to Cortana (Taskbar) -> Settings (Gear Icon) -> "Taskbar tidbits" to off
I wouldn't use the built in "Mail" app with or without ads, it is terrible. Just have him simply not use it.