This post must sound like amateur hour right now.
At 8:50, the presenter has created a Pawn blueprint with a static mesh component, spring-arm and camera called Demo Tank. He creates a GameMode called Tank_Game and sets the World Settings GameMode to it. Then he sets the pawn to Demo Tank, presses Run and voila! The game is running using the Tank pawn.
It seems that many vehicle tutorials out there begin the same way.
I start a blank project, follow the same steps and I still find myself controlling the default pawn from the start location.
What am I doing wrong?